High power ion beam generator systems and methods

ABSTRACT

Provided herein are high energy ion beam generator systems and methods that provide low cost, high performance, robust, consistent, uniform, low gas consumption and high current/high-moderate voltage generation of neutrons and protons. Such systems and methods find use for the commercial-scale generation of neutrons and protons for a wide variety of research, medical, security, and industrial processes.

The present application is a continuation of U.S. application Ser. No.15/873,664, filed Jan. 17, 2018, which claims priority to U.S.Provisional application Ser. No. 62/447,685, filed Jan. 18, 2017, eachof which is herein incorporated by reference in its entirety.

FIELD

Provided herein are high energy ion beam generator systems and methodsthat provide low cost, high performance, robust, consistent, uniform,high efficiency, and high current/high-moderate voltage generation ofneutrons and protons. Such systems and methods find use for thecommercial-scale generation of neutrons and protons for a wide varietyof research, medical, security, and industrial processes.

BACKGROUND

Particle accelerators are devices that energize ions and drive them intoa target. Neutron generators are a specific use of particle acceleratorthat produce neutrons by fusing isotopes of hydrogen. A fusion reactiontakes place by accelerating either deuterium, tritium or a mixture ofthe two isotopes into a target that also contains deuterium, tritium ora mixture of the isotopes. Fusion of deuterium atoms results half of thetime in formation of a ³He ion and a neutron, the other half resultingin the formation of a ³H (tritium) ion and a proton. Fusion of adeuterium and a tritium atom results in the formation of a ⁴He ion and aneutron.

Particle accelerators and neutron generators have numerous applicationsin medicine, imaging, industrial processes (e.g., on-line analyzers,metal cleanliness, raw materials, Al base catalysts, energy production),material analysis, safeguards (e.g., nuclear material detection),research, education, exploration, security (e.g., explosive detection,chemical weapon detection, contraband detection), and ion implantation.

Historically, neutron generation has involved incredibly complex andexpensive systems and employed approaches that either generate or useundue levels of hazardous materials or provide insufficient neutronoutput to satisfy commercial needs. Radioactive sources capable ofproducing high neutron levels contain hazardous quantities of radiationrequiring many safety considerations. Neutrons can also be produced bynuclear reactions with accelerators (e.g., cyclotrons, Van de Graaffaccelerators, LINAC) with large yields, but at substantial cost andcomplexity of operation. Use of neutron generators usingdeuterium-tritium (DT) reactions addressed some of the safety problems,but required sealing because of tritium content and have a typicallyshort lifetime. Attempts at using deuterium-deuterium (DD) neutrongenerators have met with limited success because of the ˜100× lowerfusion cross section of the DD reaction compared to the DT reaction.

The cost, lack of efficiency, safety concerns, and lack of durability ofexisting systems has kept them from finding use in many commercialapplications that could benefit from neutron generators. Addressingthese problems in this field has been very complex and routineoptimization or alteration of existing systems has failed to providemeaningful or practical solutions.

SUMMARY

Provided herein are high energy ion beam generator systems and methodsthat provide low cost, high performance, robust, consistent, uniform,low gas consumption, low fuel consumption, and highcurrent/high-moderate voltage neutron and proton generation. The systemsand methods provide a balance of throughput, cost, and reliabilitypreviously unachieved. Such systems provide viable commercial-scaleneutron and proton generation for commercial processes such assemi-conductor and LED manufacture, among many others.

Multiple performance enhancing technologies are described herein thatindividually and collectively contribute to the high performing highenergy ion beam generator systems and methods. It should be understoodthat unless expressly stated otherwise or contrary to logic each of thetechnologies described herein may be used in combination with each otherto provide generators with desirable performance features andcharacteristics. The technologies are grouped, for convenience, withinthe following categories: I) ion source technologies; II) infrastructuretechnologies; III) high voltage systems technologies; IV) neutronproducing target technologies; V) automated control system technologies;and VI) exemplary applications and indications. Particular technologieswithin each group and between groups may be used in combination.

Individually or collectively these technologies may be applied to anyhigh energy ion beam generator system having the relevant components. Toillustrate embodiments of the technology, many of the features aredescribed in the context of high energy ion beam generators employed byPhoenix Nuclear Labs, LLC (Monona, Wis.), see e.g., U.S. Pat. Publ. No.2011/0096887, 2012/0300890, and 2016/0163495 and U.S. Pat. Nos.8,837,662 and 9,024,261, herein incorporated by reference in theirentireties. However, it should be understood that these technologies maybe applied to a wide range of high energy ion beam generators andcomponent parts thereof including those by Pantechnik (Bayeux, France),D-Pace (British Columbia, Canada), Adelphi Tech Inc. (Rosewood City,Calif.) (see e.g., U.S. Pat. Publ. No. 2014/0179978, herein incorporatedby reference in its entirety), Starfire Industries, LLC (Champaign,Ill.) (see e.g., U.S. Pat. No. 9,008,256, herein incorporated byreference in its entirety), Thermo Fisher Scientific (see e.g., U.S.Pat. No. 8,384,018, herein incorporated by reference in its entirety),and Sodern (Limeil-Brevannes, France).

Uses for such systems include, but are not limited to, semiconductormanufacture (e.g., silicon cleaving for photovoltaic semiconductorapplications), isotope production and separation, cyclotron injectionsystems, accelerator mass spectrometry, security (e.g., explosivesdetection), industrial diagnostics and quality control, and imaging.Cyclotrons are widely used across medical and industrial fields. Ionbeams are used in a wide range of settings in the semiconductorindustry. Better ion sources translate to cheaper, more efficient, andmore effective production techniques for circuit components that are thebuilding blocks of all modern IC-based technologies. In another example,negative ion sources find use in the field of magnetic confinementfusion energy.

For decades scientists have sought to develop an energy source based onnuclear fusion reactions, as it could potentially provide an essentiallyunlimited amount of clean energy with virtually no harmful byproducts.Though fusion energy technologies have advanced immensely over the pastseveral decades, there are still a number of technical challenges thathave prevented the development of a clean fusion energy reactor. Onechallenge faced by fusion energy is unreliable high current negative ionsources. Existing negative ion fusion injectors use filaments and/ormagnetically coupled plasmas that suffer from many of the deficienciesdiscussed herein. A reliable, long lifetime negative ion sourcedrastically increases the ion source conversion efficiency, lifetime,reliability, and current output.

In some embodiments, provided herein are devices comprising: a) awaveguide comprising: i) a proximal end comprising an electromagneticwave entry point, ii) a distal end comprising an electromagnetic waveexit point, and iii) outer walls extending between the proximal end andthe distal end and configured to propagate electromagnetic waves; and b)an inverted impendence matching component located inside the waveguidecomponent, wherein the inverted impedance matching component extendsfrom the distal end of the waveguide to at least partway towards theproximal end of the waveguide, and wherein the inverted impedancematching component comprises a distal end and a proximal end, whereinthe distal end of the impedance matching component is located at or nearthe distal end of the waveguide and has a greater cross-sectional areathan the proximal end of the inverted impedance matching component.

In certain embodiments, the inverted impedance matching componentcomprises metal. In further embodiments, the inverted impedance matchingcomponent is configured to be cooled by water. In other embodiments, theinverted impedance matching component is located along the midline ofthe waveguide. In additional embodiments, the inverted impedancematching component is supported by one or more support legs attached tothe outer walls of the wave guide. In certain embodiments, theelectromagnetic waves are microwaves. In further embodiments, thecross-sectional area at the distal end of the inverted impedancematching component is at least two times, or three times, or four times,as large as the cross-sectional area at the proximal end of the invertedimpedance matching component. In some embodiments, the invertedimpedance matching component comprises one or more steps (e.g., 2, 3, 4,5, 6, 7 . . . 10 . . . or 20) that allow the cross-sectional area tochange from the proximal to the distal ends of the inverted impedancematching component.

In further embodiments, the inverted impedance matching componentcomprises a taper from the proximal to the distal ends of the invertedimpedance matching component that thereby allows the cross-sectionalarea to change. In certain embodiments, the cross-sectional area at thedistal end of the inverted impedance matching component is large enoughto block all or nearly all back flowing electrons when the device ispart of an accelerator system.

In particular embodiments, provided herein are systems comprising: a) anelectromagnetic wave source; b) a plasma chamber; and c) the devicedescribed above (and herein) composed of a waveguide and invertedimpedance matching component. In some embodiments, the proximal end ofthe waveguide is operably attached to the electromagnetic wave source,and wherein the distal ends of the waveguide is operably attached to theplasma chamber. In further embodiments, the electromagnetic wave sourcecomprises a microwave source.

In some embodiments, provided herein are systems comprising: a) acomputer processor; b) non-transitory computer memory comprising one ormore computer programs and a database, wherein the one or more computerprograms comprises accelerator system monitoring and/or optimizationsoftware, and c) an accelerator system that generates a high-energy ionbeam (e.g., that generates neutrons or protons) comprising one or moreof the following sub-systems which are in operable communication withthe non-transitory computer memory, and which can be automaticallyadjusted by the accelerator system monitoring and/or optimizationsoftware: i) an ion source and an ion source monitoring component; ii) afocus solenoid magnet and a focus solenoid magnet monitoring component;iii) a tube aperture and a tube aperture monitoring component; iv) asolid or gas target and a solid or gas target monitoring component; v)an ion beam extraction and secondary electron suppression component andan extraction and suppression monitoring component; vi) a beamgenerating sub-system and beam generating sub-system monitoringcomponent; vii) a beam focusing and steering sub-system and beamfocusing and steering sub-system monitoring component; viii) anaccelerator/resistor sub-system and accelerator/resistor sub-systemmonitoring component; ix) a beam steering sub-system and a beam steeringsub-system monitoring component; and x) pressurized gas sub-systemcomponent and a pressurized gas sub-system component monitoringcomponent.

In certain embodiments, 1) the ion source monitoring component comprisesa mass flow meter, thermocouple, coolant flow meter, and/or a pressuregauge; 2) the focus solenoid monitoring component comprises athermocouple, coolant flow meter, voltage monitor, and/or currentmonitor; 3) the tube aperture monitoring component comprises a camera,thermocouples, and/or a coolant flow meter; 4) the solid or gas targetmonitoring component comprises a camera, thermocouple, coolant flowmeter, and/or radiation detector; 5) the extraction and suppressionmonitoring component comprises a pressure gauge, a thermocouple, acurrent monitor, and/or a voltage monitor; 6) the beam generatingsub-system monitoring component comprises a current monitors and/oremittance scanner; and 7) the a pressurized gas sub-system componentmonitoring component comprising a pressure gauges and/or gas analyzer.

In particular embodiments, the accelerator system monitoring and/oroptimization software is configured to collect and analyze a pluralityof different set-points of the sub-systems and calculate optimizedsetting for such sub-systems. In other embodiments, the acceleratorsystem monitoring and/or optimization software is configured to changethe set points on one or more of the sub-systems to at least partiallyoptimize performance of the accelerator system.

In some embodiments, provided herein are systems comprising: a) an ionsource plasma chamber, wherein the plasma chamber has a source axisalong the direction of a beam exiting the plasma chamber, b) at leastone ion source magnet (e.g., solenoid or permanent magnet), wherein theat least one ion source magnet comprises an opening and at least oneouter wall, wherein the ion source plasma chamber extends through theopening of the at least one ion source magnet; c) at least one receivingcomponent attached to, or integral with, the at least one outer wall ofthe at least one ion source magnet; d) a ferromagnetic enclosure,wherein the at least one ion source magnet and the ion source plasmachamber are inside the ferromagnetic enclosure, wherein the at least oneion source magnet is able to move to a plurality of different positionsinside the ferromagnetic enclosure along the source axis of the plasmachamber; wherein ferromagnetic enclosure comprises at least onelongitudinal opening that extends along the direction of the source axisand aligns with the receiving component; and e) at least one adjustmentcomponent configured to extend through the longitudinal opening andattach to the receiving component, wherein the at least one adjustmentcomponent is able to secure the at least one ion source magnet at theplurality of different positions inside the ferromagnetic enclosure.

In certain embodiments, the receiving component comprises a threadedmetal connector, or snap receiver or pin hole. In particularembodiments, the adjustment component comprises a threaded bolt. Inother embodiments, the receiving component is glued to the at least oneion source magnet (e.g., solenoid magnet or permanent magnet). In someembodiments, the at least one ion source magnet is at least partiallyencased in epoxy. In other embodiments, at least one ion source magnetcomprises two or three or four ion source magnets. In additionalembodiments, the at least one longitudinal opening comprises at leasttwo, three, or four longitudinal openings.

In some embodiments, provided herein are methods comprising: a)providing a system as described immediately above, or elsewhere herein;b) moving the at least one ion source magnet (e.g., solenoid magnet orpermanent magnet) from a first position among the plurality of positionsto a second position among the plurality of positions, c) inserting theat least one adjustment component through the at least one longitudinalopening into the at least one receiving component; and d) securing theat least one adjustment component to the at least one receivingcomponent, thereby securing the at least one ion source magnet in thesecond position. In certain embodiments, the at least one ion sourcemagnet comprises first and second ion source magnets, and wherein boththe first and second ion source magnets are moved from a first positionto a second position, and secured in the second position.

In some embodiments, provided herein are articles of manufacturecomprising: a metallic assembly of an accelerator system that generatesa high-energy ion beam, wherein the metallic assembly, when positionedin the accelerator system partially intercepts the high-energy ion beam,and wherein the metallic assembly comprises: a first metal component, asecond metal component, and filler metal, wherein the filler metalattaches the first metal component to the second metal component at ajoint (e.g., brazed joint).

In certain embodiments, provided herein are articles of manufacturecomprising: a metallic assembly of an accelerator system that generatesa high-energy ion beam, wherein the metallic assembly, when positionedin the accelerator system: i) partially intercepts the high-energy ionbeam, and ii) is in a vacuum environment, and wherein the metallicassembly comprises: i) at least one water cooling channel, and ii) afirst metal component, a second metal component, and filler metal,wherein the filler metal attaches the first metal component to thesecond metal component at a joint (e.g., brazed joint).

In particular embodiments, the first and second metal componentscomprise highly thermally conductive metal (e.g., copper, aluminum,etc.). In certain embodiments, the filler metal has a lower meltingpoint than the first and second metal components. In particularembodiments, the first metal component comprises a tube plate and thesecond metal component comprises a plate plug. In particularembodiments, the filler metal comprises BNi-7 alloy, BNi-6 alloy, Pd₁₀₀,Pt₁₀₀, Ni₁₀₀, or other metals or alloys suitable for brazing togetherthe first and second metal components. In certain embodiments, the firstmetal component comprises a first item selected from the groupconsisting of: a first tube, a tube cap, a different tube plate, and avalve, and wherein the second metal component comprises a second itemselected from the group consisting of: a second tube, a tube cap, adifferent tube plate, and a valve. In certain embodiments, the at leastone water cooling channel comprises at least two water cooling channels(e.g., 2, 3, 4, 5, 6 . . . 10 . . . or 25 water cooling channels).

In additional embodiments, provided herein are systems comprising: a) anaccelerator system that generates an ion beam (e.g., high-energy ionbeam); and b) a metallic assembly, wherein the metallic assembly ispositioned in the accelerator system such that it: i) partiallyintercepts the high-energy ion beam, and ii) is in a vacuum environment,and wherein the metallic assembly comprises a first metal component, asecond metal component, and filler metal, wherein the filler metalattaches the first metal component to the second metal component at ajoint (e.g., a brazed joint).

In some embodiments, provided herein are systems comprising: a) anaccelerator system that generates an ion beam (e.g., high-energy ionbeam); and b) a metallic assembly, wherein the metallic assembly ispositioned in the accelerator system such that it: i) partiallyintercepts the high-energy ion beam, and ii) is in a vacuum environment,and wherein the metallic assembly comprises: i) at least one watercooling channel, and ii) a first metal component, a second metalcomponent, and filler metal, wherein the filler metal attaches the firstmetal component to the second metal component at a joint (e.g., a brazedjoint).

In certain embodiments, provided herein are methods comprising: a)attaching a first metallic component to a second metallic component witha filler metal using a brazing technique to generate a metallicassembly, and b) inserting the metallic assembly into an acceleratorsystem that generates a high-energy ion beam, wherein the metallicassembly is positioned to partially intercept the high-energy ion beam.

In some embodiments, the metallic assembly further comprises at leastone water cooling channel. In other embodiments, the metallic assemblyis further positioned such that it is in a vacuum environment.

In some embodiments, provided herein are systems comprising: a) a highvoltage dome; b) an ion source plasma chamber located inside the highvoltage dome; c) an extraction component that is operably linked to theion source plasma chamber; and d) a gas removal sub-system comprising:i) an exhaust component located inside the high voltage dome; ii) aninsulating hose, wherein a first part of the insulating hose is locatedinside the high voltage dome and a second part of the insulating hose islocated outside of the high voltage dome in an area of lower voltage;iii) a first vacuum pump located inside the high voltage dome andoperably linked to the exhaust component and the extraction component,wherein the first vacuum pump is configured to remove gas from theextraction component and deliver the gas to the exhaust component; andiv) a second vacuum pump located inside the high voltage dome andoperably linked to the exhaust component, wherein the second vacuum pumpis configured to receive the gas from the exhaust component at a firstpressure and deliver the gas to the insulating hose at a secondpressure, wherein the second pressure is higher than the first pressure.

In certain embodiments, the system further comprises e) an outerpressure vessel, wherein the high voltage dome, the ion source plasmachamber, the extraction component, the exhaust component, the firstvacuum pump, the second pump, and at least part of the insulating hoseare located in the outer pressure vessel. In other embodiments, theinsulating hose is configured to vent the gas to the atmosphere. In someembodiments, the gas is non-ionized gas. In other embodiments, thenon-ionized gas is deuterium gas. In certain embodiments, the systemfurther comprises the gas. In particular embodiments, the gas isnon-ionized gas. In additional embodiments, the insulating hose has ahelix shape. In further embodiments, the insulating hose has about 20-30helix shaped turns, and is about 5-15 feet in length. In otherembodiments, the first vacuum pump comprises a pump selected from thegroup consisting of: a turbomolecular pump, a cryopump, an ion pump, anda high vacuum pump. In some embodiments, the second vacuum pumpcomprises a roughing pump. In other embodiments, the system furthercomprises: e) an inner pressure vessel located inside the high voltagedome, wherein the second vacuum pump is located in the inner pressurevessel, and wherein the following components are not located in the pumppressure vessel: the high voltage dome, the ion source plasma chamber,the extraction component, and the first vacuum pump.

In some embodiments, provided herein are gas removal sub-systemsconfigured to be introduced into a high-energy ion beam generatingsystem having a high voltage dome and an extraction componentcomprising: a) an exhaust component configured to be located inside thehigh voltage dome; b) an insulating hose, wherein a first part of theinsulating hose is configured to extend through an opening in the highvoltage dome; c) a first vacuum pump configured to be located inside thehigh voltage dome and configured to be operably linked to the exhaustcomponent and the extraction component, wherein the first vacuum pump isconfigured to remove gas from the extraction component and deliver thegas to the exhaust component; and d) a second vacuum pump locatedconfigured to be located inside the high voltage dome and configured tobe operably linked to the exhaust component, wherein the second vacuumpump is configured to receive the gas from the exhaust component at afirst pressure and deliver the gas to the insulating hose at a secondpressure, wherein the second pressure is higher than the first pressure.

In particular embodiments, provided herein are methods comprising: a)providing the system above or otherwise described herein; and b)activating the gas removal sub-system such that gas present in theextraction component is: i) removed by the first vacuum pump to theexhaust component, ii) received by the second vacuum pump from theexhaust component at a first pressure, and delivered to the insulatinghose at a second pressure that is higher than the first pressure, andiii) delivered by the insulating hose to atmosphere. In someembodiments, the gas in the extraction component is non-ionized gas thathas traveled from the ion source plasma chamber to the extractioncomponent.

In some embodiments, provided herein are systems comprising: a) an outerpressure vessel; b) an inner pressure vessel located inside the outerpressure vessel; c) an exhaust component located inside the outerpressure vessel, wherein a portion of the exhaust component is alsolocated in the inner pressure vessel; d) an insulating hose locatedinside the outer pressure vessel, wherein a portion of the insulatinghose is also located in the inner pressure vessel; e) a first vacuumpump located inside the outer pressure vessel and operably linked to theexhaust component; and f) a second vacuum pump located inside the innerpressure vessel and operably linked to the exhaust component.

In certain embodiments, the outer pressure vessel comprises gas at ahigher pressure than gas in the inner pressure vessel. In someembodiments, the gas in the inner pressure vessel is at aboutatmospheric pressure. In further embodiments, the first vacuum pump isconfigured to be operably linked to an extraction component of anaccelerator system that generates a high-energy ion beam, and whereinthe first vacuum pump is configured to remove gas from the extractioncomponent and deliver the gas to the exhaust component. In additionalembodiments, the second vacuum pump is configured to receive the gasfrom the exhaust component at a first pressure and deliver the gas tothe insulating hose at a second pressure, wherein the second pressure ishigher than the first pressure. In certain embodiments, the systemfurther comprises an extraction component. In further embodiments, thesystem further comprises an ion source plasma chamber located inside theouter pressure vessel. In some embodiments, the extraction component isoperably linked to the ion source plasma chamber.

In some embodiments, provided herein are systems comprising: a) at leastone high voltage component that is held at high voltage in anaccelerator system that generates a high-energy ion beam, and b) anelectrical power component that is electrically linked (and/ormechanically linked) to the at least one high voltage component, whereinthe electrical power component provides electrical power to the at leasthigh voltage component (e.g., in a manner that is electrically isolatedfrom ground), wherein the electrical power component comprises a V-belt,and wherein the V-belt comprises a plurality of segments (e.g., 3 . . .25 . . . 100 . . . 400 segments) and is: i) a poor electrical conductor,or ii) a non-electrical conductor.

In further embodiments, the V-belt comprises a polyester-polyurethanecomposite. In certain embodiments, the electrical power componentfurther comprises a motor and a power generator. In additionalembodiments, the electrical power component further comprises a firstV-belt pulley operably attached to the motor, and a second V-belt pulleyoperably attached to the power generator. In some embodiments, the atleast one high voltage component comprises an ion source plasma chamber.

In some embodiments, provided herein are systems comprising: a) anaccelerator sub-system that generates a high-energy ion beam, whereinthe accelerator system comprises: i) an ion source plasma chamber, ii) amicrowave generating component which generates microwaves, iii) a powersource operably linked to the microwave generating component, iv) awaveguide positioned to receive the microwaves and deliver them to theion source plasma chamber, wherein when the microwaves contact a gas inthe ion plasma chamber to generate a source of ions; v) an ion beamextraction component that is operably linked to the ion source plasmachamber to extract a low-energy ion beam from the ion plasma chamber,iv) an accelerator component comprising an accelerator column, anaccelerator entrance opening for receiving a low-energy ion beam, and anaccelerator exit opening for delivering a high-energy ion beam; and b) apower modulating component operably linked to the power source, whereinthe power modulating component is configured to modulate power flowingfrom the power source to the microwave generating component such thatthe microwaves entering the waveguide are rapidly pulsed and/orextinguished/generated, thereby rapidly pulsing and/orextinguishing/generating the high-energy ion beam. In certainembodiments, the accelerator system is a direct-injection acceleratorsystem. In other embodiments, the microwave generating componentcomprises a magnetron.

In particular embodiments, provided herein are methods comprising: a)providing the systems described above (and herein), and b) activatingthe accelerator sub-system and the power modulating component such thatthe high-energy ion beam is generated and the high-energy ion beam israpidly pulsed and/or extinguishing/generated.

In some embodiments, provided herein are methods comprising: a)positioning, in a direct-injection accelerator system that generates ahigh-energy ion beam, an ion beam generating component a first distancefrom an accelerator entrance of an accelerator column, and b)positioning the an ion beam generating component a second distance froman entrance of an accelerator column, wherein the second distance isdifferent from the first distance, and wherein the second distanceimproves the performance of the direct injection accelerator system. Incertain embodiments, the first and second distances are within the rangeof 10-500 mm.

In some embodiments, provided herein are systems comprising: a) adirect-injection accelerator sub-system that generates a high-energy ionbeam, wherein the accelerator system comprises: i) an ion source plasmachamber, ii) a microwave generating component which generatesmicrowaves, iii) a power source operably linked to the microwavegenerating component, iv) a waveguide positioned to receive themicrowaves and deliver them to the ion source plasma chamber, whereinwhen the microwaves contact a gas in the ion plasma chamber a ion beamis generated; v) an extraction component that is operably linked to theion source plasma chamber, iv) an accelerator component comprising anaccelerator column and an accelerator entrance opening for receiving theion beam; and b) a vacuum component, wherein the vacuum component isoperably linked to the extraction component and/or the acceleratorcomponent, wherein the vacuum component is configured to reduce pressurein the extraction component and/or the accelerator component. Inparticular embodiments, the reduction in pressure is at a level thatreduces the diameter of the high-energy ion beam.

In some embodiments, provided herein are methods comprising: a)providing the systems described above (and herein), and b) activatingthe direct-injection accelerator sub-system and the vacuum componentsuch that the high-energy ion beam is generated such that thehigh-energy ion beam has a smaller diameter than it would have in theabsence of the reduction in pressure.

In some embodiments, provided herein are systems comprising: a) anaccelerator sub-system that generates a high-energy ion beam, whereinthe accelerator system comprises: i) a high voltage dome; ii) an ionbeam generating component which is located inside the high voltage dome,and iii) an accelerator component comprising an accelerator column; andb) a water resistor sub-system comprising: i) a water circulatingcomponent comprising water piping and a water reservoir, ii) a waterresistor element that runs along the accelerator column, wherein thewater resistor element comprises electrically non-conductive and/orinsulated tubing fluidically linked to, or integral with, the waterpiping such that controlled conductivity water circulating in the watercirculating component passes through the water resistor element.

In certain embodiments, the system further comprises the controlledconductivity water, wherein the controlled conductivity water comprises:i) deionized water, 2) deionizing (DI) resin, and a metal salt. Infurther embodiments, the accelerator component further comprises aplurality of grading rings that run along the accelerator column. Inadditional embodiments, the insulating tubing comprises a materialselected from the group consisting of: polycarbonate, polymethylmethacrylate (PMMA), and polyethylene. In further embodiments, the watercirculating component further comprises a water pump, a heat exchangerand/or a DI resin source component. In some embodiments, the controlledconductivity water contains a sufficient amount of the DI resin suchthat the deionized water has a resistivity of 15 Megohm-cm or higher. Infurther embodiments, the metal salt is selected from the groupconsisting of: copper sulfate, sodium chloride, ammonium chloride,magnesium sulfate, and sodium thiosulfate. In further embodiments, thewater resistor element is able to withstand voltages of up to about 300kV DC, and reject up to about 30 kW, or up to about 3 kW, or up to about5 kW, of heat.

In particular embodiments, provided herein are methods comprising: a)providing the systems above (and as described herein), and b) activatingthe accelerator sub-system and the water-resistor sub-system such that,while the high-energy ion beam is generated, the controlled conductivitywater circulates through the water circulating component and thewater-resistor element performs as an electrical resistor along theaccelerator column.

In other embodiments, provided herein are systems comprising: a) atleast one high-voltage power supply (HVPS) configured to deliver powerto a component of an accelerator sub-system that generates a high-energyion beam; and b) a water resistor sub-system comprising: i) a watercirculating component comprising water piping and a water reservoir, andii) a water resistor element comprising an electrically non-conductiveand/or insulated tubing fluidically linked to, or integral with, thewater piping such that controlled conductivity water circulating in thewater circulating component passes through the water resistor element.

In particular embodiments, provided herein are methods comprising: a)providing the systems described above (and as described herein), and b)testing the at least one HVPS using the water resistor sub-system as atest load.

In some embodiments, provided herein are methods of designing lensescomprising: a) entering the following parameters at the plasma lensaperture of an accelerator system into a software application: beamcurrent, extraction voltage, ion species fractions, maximum electricfield, and ion current density; b) receiving an output from the softwarefor a design of at least one lens in an electrostatic lens stack,wherein the electrostatic lens stack comprises: a plasma lens, anextraction lens, a suppression lens, and an exit lens; and c)fabricating the at least one lens based on the output. In certainembodiments, the software application comprises the PBGUNS softwareapplication. In further embodiments, the at least one lens comprises atleast two, at least three, or all four of the lenses in theelectrostatic lens stack. In further embodiments, the methods furthercomprise entering at least one of the following into the softwareapplication: grid precision, an empirically determined beamneutralization factor, and the electron and ion temperatures in thesource plasma.

In some embodiments, provided herein are systems (e.g., for use in, orpart of, a high energy ion beam generator system) comprising anextraction lens stack having a plurality of insulating balls (e.g.,alumina ceramic, aluminum nitride, sapphire, diamond, or other oxide ornon-oxide ceramic balls) positioned between lens gaps of the extractionlens stack. In some embodiments, a minimum of three insulating balls arepositioned between each lens gap. In some embodiments, the threeinsulating balls are spaced evenly in azimuthal coordinate. In someembodiments, the lens stack is held together with metal bolts. Furtherprovided herein are methods of generating neutrons and protons usingsuch systems so as to provide, for example, enhanced mechanicalstability, beam quality, and protection of source and beamlinecomponents, while increasing the total current that can be reliablytransported to the target of interest.

In some embodiments, provided herein is a system (e.g., for use in, orpart of, a neutron generator system) comprising: a) a high power densitysolid target comprising a reactive species (e.g., reactive hydrogenspecies such as deuterium or tritium) embedded in a solid matrix; and b)a cooling component. The solid matrix may be made of any desiredmaterial including, but not limited to, titanium.

In some embodiments, the cooling component is a closed-loop component.In some embodiments, a coolant flow pathway is integrated into the solidtarget. In some embodiments, the system further comprises a source ofcoolant, providing coolant that is flowed through the cooling component.In some embodiments, the coolant is selected from the group consistingof water, glycol (e.g., (poly-)ethylene glycol), oil, helium, or thelike. In some embodiments, the closed-loop component comprises adeionization sub-component to deionize coolant flowing therethrough. Insome embodiments, the closed-loop component comprises a filteringsub-component to filter coolant flowing therethrough. In someembodiments, the coolant component comprises a chiller positioned topre-cool coolant prior to contact with the target.

In some embodiments, the target is manufactured with a thin wall so asto maximize the impact of the coolant. In some embodiments, the wall hasa thickness of 0.02 inches or less (e.g., 0.01 inches). In someembodiments, the wall is composed of a material selected from the groupconsisting of copper, silver, gold, diamond, diamond like carbon, or acombination thereof.

In some embodiments, the target comprises a pathway with convolutions toincrease surface area relative to a target lacking the convolutions. Insome embodiments, the convolutions are fins or ribs or combinationsthereof.

In some embodiments, the cooling component is configured for laminarflow of coolant. In some embodiments, the cooling component compriseschannels having irregular surface features (e.g., dimples, spiraledindentions, or combinations thereof). In some embodiments, the coolingcomponent is configured for turbulent flow of coolant, with channelshaving irregular surface features (e.g., dimples, spiraled indentions,or combinations thereof).

Method of employing such systems are also provided. For example, in someembodiments, a method of generating neutrons with a high power densitysolid target is provided by using any of the above systems. In someembodiments, the method involves depositing an ion beam's energy into asmall volume.

In some embodiments, provided herein is a system (e.g., for use in, orpart of, a neutron generator system) comprising: a) a solid target; b) avacuum system; and c) a source of a noble gas in fluid communicationwith the vacuum system and configured to release noble gas near thesolid target. In some embodiments, the noble gas is argon. Furtherprovided herein are methods of cleaning a neutron generator solid targetcomprising: exposing the solid target to a noble gas (e.g., while thesolid target is exposed to an ion beam). In some embodiments, the noblegas is flowed at 1 to 10 standard cubic centimeters per minute.

In some embodiments, provided herein is a system (e.g., for use in, orpart of, a neutron generator system) comprising: a) an accelerator thatproduces an ion beam; b) a target (e.g., gas target) positioned to becontacted by the ion beam; c) a target aperture separating theaccelerator and the target; d) a focusing component that focuses the ionbeam to the aperture; and e) a plurality of thermal sensors positionednear an upstream-facing surface of the target aperture. In someembodiments, the plurality of thermal sensors comprises four thermalsensors equally spaced at 90 degree intervals about an axis of theaperture. In some embodiments, the thermal sensors comprisethermocouples (e.g., copper-constantan thermocouples). In someembodiments, the thermal sensors are platinum resistance temperaturedetectors (RTDs), thermistors, or semiconductor temperature sensors.

In some embodiments, the system further comprises a processor thatreceives temperature signals from the sensors. In some embodiments, theprocessor sums temperature signals from the sensors and generates anaverage target aperture temperature. In some embodiments, the processoradjusts the ion beam position based on the average target aperturetemperature to minimize the temperature of the target aperture.

Further provided herein are methods of steering an ion beam to a targetaperture in a neutron generator system comprising: a) measuringtemperature at a plurality of locations around said target aperture; andb) steering the position of the ion beam to minimize temperature at thetarget aperture (e.g., using the above systems).

In some embodiments, provided herein is a system (e.g., for use in, orpart of, a neutron generator system) comprising: a) an accelerator thatproduces an ion beam; b) a target (e.g., gas target) positioned to becontacted by the ion beam; c) a target aperture separating theaccelerator and the target; and d) a reverse gas jet that increasespressure differential across the aperture. In some embodiments, thereverse gas jet comprises a throat gap, a nozzle having a nozzle angleand nozzle length, and a plenum. In some embodiments, the reverse gasjet comprises a nozzle that diverges after it converges. In someembodiments, the reverse gas jet comprises a nozzle aperture ofapproximately ⅜ inch. In some embodiments, the reverse gas jet comprisesa throat gap of less than 0.01 inch. In some embodiments, the reversegas jet comprises a nozzle angle of 12.5 degrees. Further providedherein are methods of increasing a pressure differential across a targetaperture of a neutron generator comprising employing a reverse gas jetat the target aperture.

In some embodiments, provided herein is a system (e.g., for use in, orpart of, a neutron generator system) comprising a beam scraper whereinthe beam scraper is moveable into a path of an ion beam using a motor,wherein the motor is mounted to the generator system outside of a vacuumvessel containing the target. In some embodiments, the motor isconnected to the beam scraper via a magnetically coupled vacuumfeedthrough (e.g., linear motion feedthrough). In some embodiments, themotor, beam scraper, and connections there between are all-metal withbrazing manufacture. Further provided herein are methods of blocking afraction of an ion beam hitting a target in a neutron generator,comprising: moving a beam scraper into a position contacted by the ionbeam using a motor that is mounted to the generator outside of a vacuumvessel containing the target.

In some embodiments, provided herein is a system comprising: a) a highenergy ion beam generator device having a first interlock; and b) a usercontrol station having a second interlock, wherein the high energy ionbeam generator and the user control station are connected via a fiberoptic interlock comprising a plurality of normally-closed switches in aseries loop that remain closed to indicate that the generator is safe tooperate, a number of normally-open switches in a parallel loop thatremain open to indicate that the generator is safe to operate, or boththe series loop and said parallel loop. In some embodiments, the highenergy ion beam generator and the user control station are electricallyisolated from one another. In some embodiments, the fiber opticinterlock comprises a frequency generator. In some embodiments, thefrequency generator triggers a fiber-optic transmitter causing light topulse at a set frequency. In some embodiments, the system isconfigurable among a plurality of distinct frequencies, for example, forthe purpose of having multiple channels with non-interoperabilitybetween channels to prevent erroneous cross-connection. In someembodiments, the system comprises control software that manages thefiber optic interlock. In some embodiments, the control softwareoperates a multiple-signal verification procedure of the fiber opticinterlock. Methods of using such a system are also provided. In someembodiments, the method comprises transmitting information via the fiberoptic interlock to or from the high energy ion beam generator and usercontrol station to the other.

In some embodiments, provided herein is a system (e.g., for use in, orpart of, a high energy ion beam system) comprising: a) a high energy ionbeam generator device that produces a beam, and b) a damage mitigationcomponent, the damage mitigation component comprising: i) a plurality ofsensors positioned on the device and configured to monitor a pluralityof regions of that device that may interact with the beam; and ii)control software in communication with the plurality of sensors andconfigured to generate an alert or alarm and adjust the device inresponse to the alert or alarm. In some embodiments, one or more of thesensors measures temperature of a region of the device. In someembodiments, one or more of the sensors measures coolant (e.g., water)flow rate. In some embodiments, one or more of the sensors are incontinuous sensing mode. In some embodiments, one or more or all of thesensors has associated therewith a threshold value that if exceededgenerates the alert or alarm. In some embodiments, the alert comprises auser warning. In some embodiments, the alarm triggers a device shut downor reset. In some embodiments, the alarm is a latching alarm thatrequires a user to reset the device prior to further operation. In someembodiments, the control software filters out background EMI. In someembodiments, the filtered background EMI is under a predefined thresholdduration or frequency to differentiate it from a potentially harmfulevent. Methods of using the system are also provided. In someembodiments, methods comprise detecting potential damage events usingthe system. In some embodiments, the methods comprise generating analert or alarm and desired associated response (e.g., warning, automaticsystem shut down, etc.).

In some embodiments, provided herein is a system (e.g., for use in, orpart of, a high energy ion beam generating system) comprising: a) a highenergy ion beam generator device, and b) an arc down mitigationcomponent, the arc down mitigation component comprising: i) a pluralityof sensors positioned on the device and configured to monitor conditionsconsistent with an arc down event; and ii) control software incommunication with the plurality of sensors and configured to generatean alert or alarm and adjust the device in response to the alert oralarm. In some embodiments, the alarm triggers an automated recoverysequence that returns the device to normal operation without userintervention. Methods of using the system are also provided. In someembodiments, methods comprise responding to arc down events using thesystem.

In some embodiments, provided herein is a high energy ion beam generatorsystem comprising a closed-loop control component that manages highvoltage power supply (HVPS) setpoint. In some embodiments, the componentalso controls one or more other system functions including but notlimited to microwave power, focus, and steering. In some embodiments,provided herein are methods for controlling high energy ion flux outputvariability in a high energy ion beam generator comprising: managinghigh voltage power supply (HVPS) setpoint with a closed-loop controlcomponent.

In some embodiments, provided herein is a neutron guidance system foruse in neutron radiography comprising a collimator comprising a highdensity polyethylene (HDPE) layer, a borated polyethylene layer, a metallayer (e.g., comprising aluminum and/or lead layers), and a cadmiumlayer.

In some embodiments, provided herein is system for neutron radiographycomprising one or more or all of: a) a neutron source (e.g., a source of2.45 MeV neutrons); b) a high density polyethylene (HDPE) layer, aborated polyethylene layer, a metal layer (e.g., comprising aluminumand/or lead layers), and a cadmium layer; c) a detector; d) a moderator(e.g., a graphite moderator and/or a D₂O moderator); and e) undergroundshielding (e.g., comprising soil, concrete, or other protective layers).In some embodiments, the system comprises an offset collimator that doesnot directly align with a fast neutron source.

Further provided herein are methods of imaging a sample comprising:exposing a sample to neutrons generated by the above systems.

In some embodiments, provided herein are systems and methods forsemiconductor manufacturing. In some embodiments, the system comprisesan accelerator system that generates a high-energy ion beam (e.g.,hydrogen ion beam) as described here having the beam directed at acomponent holding semiconductor material. In some embodiments, themethod comprises contacting a semiconductor material with protonsgenerated from a high energy ion beam generator system described herein.In some embodiments, the method further comprises the step of generatinga thin film wafer by cleaving the semiconductor material (e.g., at acleave site formed by implanted hydrogen ions). In some embodiments, themethod further comprises the step of fabricating a photovoltaic (PV)wafer from the thin film wafer. In some embodiments, the method furthercomprises the step of fabricating a solar panel comprising thephotovoltaic wafer. In some embodiments, the method further comprisesthe step of fabricating a light emitting diode (LED) comprising thephotovoltaic wafer. In some embodiments, the method comprises the stepof fabricating a light emitting diode (LED) from the thin film wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary schematic of an accelerator system where thetarget is a gas target.

FIG. 2 shows an exemplary schematic of an accelerator system where thetarget is a solid target.

FIG. 3A-B shows known waveguide designs, with metal impedance matchingcomponents (two step ridges are shown) that each extend inward from abroader face of the waveguide in the direction of its narrowerdimension. FIG. 3A shows a top: section view, while FIG. 3B shows anelectric field at each step.

FIG. 4A-B shows an exemplary waveguide design of the present disclosure,with inverted impedance matching components which extend progressivelyoutward from the midplane of the waveguide toward the broader walls ofthe waveguide. FIG. 4A shows a top: section view, while FIG. 4B shows anelectric field at each step.

FIG. 5 shows an exemplary layout of telemetry and diagnostics in anaccelerator system.

FIG. 6 shows an exemplary flowchart for automated mapping (left) andclosed loop feedback (right).

FIG. 7 shows an example of 2D slice of the ion source operational phasespace mapped by automatic algorithms.

FIG. 8 provides an exemplary embodiment of an adjustment system foradjusting and fixing solenoid magnets that surround an ion source plasmachamber.

FIG. 9A shows an exemplary differential tube assembly, with parts thatare brazed together. FIG. 9B shows a see-through view of an exemplarydifferential tube plate, showing water channels located therein. FIG. 9Cshows a perspective view of an exemplary differential tube plate.

FIG. 10 provides an exemplary schematic of gas pumping flow in a nestedpressure vessel configuration, where a roughing pump is located insidean inner (smaller) pressure vessel inside an outer (larger) pressurevessel, so that it can operate at a different pressure (e.g.,atmospheric pressure).

FIG. 11 shows an example of pulsed beam from modulating magnetron(measured with a Faraday cup), which modulates the microwaves enteringthe plasma chamber.

FIG. 12A shows an example of a simulation of beam trajectories in adirect injection, high gradient accelerator. 70 mA deuterium, 300 keVaccelerator, 39 kV extraction. The Resulting beam generally has loweremittance but larger divergence. FIG. 12B shows an example of asimulation of the same beam with drift length and electrostaticsuppression and drift region before a low-gradient accelerator. 70 mAdeuterium, 300 keV accelerator, 39 kV extraction. The resulting beam hasa larger emittance but lower divergence.

FIG. 13 shows an exemplary actively cooled water resistor system.

FIG. 14 shows an exemplary user interface for the lens design softwareapplication.

FIG. 15 shows a sample beam trajectory plot from PBGUNS.

FIG. 16 shows an exemplary use of precision ceramic balls for electricalisolation and alignment of an electron suppression element.

FIG. 17 shows one embodiment of a liquid cooled solid target featuringturbulence inducing structures comprising a plurality of parallel finswith dimpled holes to interrupt smooth surfaces. The left panel shows atop view. The right panel shows a cross-sectional view with the plane ofcross-section identified.

FIG. 18 shows an example of turbulence-inducing irregular features influid cooling channels of a solid target.

FIG. 19 shows a graph of neutron yield from a titanium-plated target asa function of time.

FIG. 20 shows an exemplary configuration of a system for focusing and/orsteering of the ion beam through the target aperture.

FIG. 21 shows a schematic of a reverse gas flow jet.

FIG. 22 shows an exemplary beam scraper configuration.

FIG. 23 shows an exemplary fiber optic interlock arrangement forcommunication between an electrically isolated high energy ion beamgenerator and a user control station.

FIG. 24 shows a schematic of a moderator, collimator, and imagingenclosure for thermal neutron radiography applications.

DETAILED DESCRIPTION

Exemplary components of the accelerator system are described in moredetail in the following sections: I. Ion Source; II. Infrastructure;III. High Voltage Systems; IV. Neutron Producing Target; V. AutomatedControl Systems; VI. Diagnostics; and VII. Uses for Accelerator Systems.

I. Ion Source

The ion source provided herein includes a number of componentsincluding: a plasma chamber microwave waveguide feed; an operationalparameter optimization technique; the source magnet mounting mechanism;and the use of brazing for manufacturing water-cooled beamlinecomponents). Each of these improvements will be discussed in turn.

A. “Inverted” Waveguides

Provided herein are waveguides that contained inverted impedancematching components (e.g., inverted in the sense that the stepped ridgesare mounted in the center of the waveguide rather than beingincorporated into the external structure) that help prevent theback-flow of electrons when positioned between an electronic magneticwave source (e.g., microwave source) and a plasma chamber (e.g., as partof a larger accelerator system). The inverted impedance matchingcomponents are generally seen to be “inverted” or “inside-out” withrespect to the conventional prior art impedance matching technique, asthe inverted components, in certain embodiments, extend progressivelyoutward from the midplane of the waveguide toward the broader walls(FIG. 4). In certain embodiments, the inverted waveguides comprises adevice comprising: a) a waveguide comprising: i) a proximal endcomprising an electromagnetic wave entry point, ii) a distal endcomprising an electromagnetic wave exit point, and iii) outer wallsextending between the proximal end and the distal end and configured topropagate electromagnetic waves; and b) an inverted impendence matchingcomponent located inside the waveguide component, wherein the invertedimpedance matching component extends from the distal end of thewaveguide to at least partway towards the proximal end of the waveguide,and wherein the inverted impedance matching component comprises a distalend and a proximal end, wherein the distal end of the impedance matchingcomponent is located at or near the distal end of the waveguide and hasa greater cross-sectional area than the proximal end of the invertedimpedance matching component.

In a microwave ion source, a plasma chamber is supplied with the desiredgas (e.g., hydrogen, deuterium, etc.), a magnetic field, and microwavepower. The microwaves are delivered to the plasma chamber through awaveguide entering the chamber at the end opposite the beam exitaperture. The magnetic field is shaped so that the electron cyclotronresonance (ECR) condition is satisfied near the beam exit aperture,i.e., the electron cyclotron frequency at that location matches thefrequency of the applied microwaves. For example, ω_(ce)=q_(B)/m where qis the electron charge, B is the magnetic flux density and m is the massof the electron.

Due to the magnetic field geometry, the microwave power may also beabsorbed in an ECR region within the waveguide before it reaches theplasma chamber. This is prevented by keeping the waveguide under vacuumand using a ceramic disk to separate it from the gas in the plasmachamber. In the art, waveguides may include a mechanism for impedancetransformation in the form of a pair of stepped ridges increasing inextent from the broad faces of the guide to reach their maximum extentat the ceramic disk, designed to reduce the impedance mismatch betweenthe waveguide and the plasma in the source chamber (see FIG. 3).

By way of background, electrons created in the extraction andacceleration regions of an accelerator system can enter the ion sourceplasma chamber through the ion beam exit aperture and impact the ceramicinsulator at the opposite end of the plasma chamber at high energies. Ifthese electrons burn a hole through the insulator, the working gas inthe plasma can flow into the waveguide, where it can absorb microwaves,resulting in plasma formation in this region. This reduces the microwavepower available for driving the ion source plasma, affects the stabilityof the ion source and lowers the maximum extractable beam current. Ifthe hole in the ceramic becomes large enough, overheating of thewaveguide may also damage that component, affecting the reliability andlifetime of the overall system.

The inverted waveguides described herein (e.g., FIG. 4) are designed tointercept back-streaming electrons which may perforate the ceramic disk,which would otherwise lead to plasma formation in the waveguide,reducing the plasma density in the source chamber and the beam currentdue to loss of microwave power, while possibly damaging the waveguidedue to excessive heating. In certain embodiments, a hole is provided inthe ceramic disk such that the electrons do not perforate the disk bydamaging it, and directly impact the impedance matching component bydesign.

Therefore, in some embodiments, provided herein inverted impedancematching components (e.g., water-cooled metal surfaces) located tointercept the back-streaming electrons without damage while efficientlycoupling microwave power into the plasma chamber. The known design ofthe waveguide step ridges is conventional in that they are electricallyand mechanically attached to the outer waveguide walls, extendingsymmetrically into the guide from the center of its broad faces, andextending for a portion of the width of the guide, as shown in FIG. 3.Due to the orientation and symmetry of the fields in the waveguide, incertain embodiments, it is possible to divide it in half along themidplane between the ridges and transpose the two halves across themidplane, as illustrated in FIG. 4. This symmetry applies at each stepof the ridges, and maintains the electrical performance of the steppeddesign to match the impedance of the waveguide to the plasma chamber.Other approaches may be used to invert the typical orientation of theimpedance matching components in a waveguide.

The resulting inverted types designs provided herein, provides asubstantial mass of metal in the path of back-streaming electrons on theaxis of the plasma chamber (see large cross-sectional area in FIG. 4B,right most section), which is supported from the sides of the chamber bya supporting component which is in a low field region and so does notperturb the microwave propagation. These support components (e.g., legs)may be, for example, solid metal for low power applications or may behollow tubes for water cooling the impedance matching component, whichmay be, for example, in the form of discrete steps as shown or may takethe form of a smoothly tapering shape.

In certain embodiments, two sets of support legs are used, as shown inFIG. 4A, with a separation such that the reflection of microwave poweraway from the plasma chamber by one support leg is largely cancelled outby the power reflected by the other support leg, with the secondreflection having equal wave magnitude and opposite wave phase.Alternatively, in some embodiments, a single support leg may be used ifthe reflection magnitude is insignificant in a low power application.

In certain embodiments, the face of the impedance matching component onwhich the back-streaming electrons are incident may be fitted with arefractory metal insert for high power applications as needed, or leftas a lower melting high thermal conductivity metal in low powerapplications.

In the prior art, the impedance matching component (e.g., which may becomposed of the two sets of metal steps (“step ridges”)) each extendinward from a broader face of the waveguide in the direction of itsnarrower dimension (FIG. 3) each half of which is translated inward byhalf the narrow dimension of the waveguide.

B. Operational Parameter Optimization

In certain embodiments, the accelerator systems or sub-systems,described here are optimized to improve performance. In general,accelerator system are composed of a large number of coupled nonlinearsubsystems. These include, but are not limited to: ion source magnetposition and current, ion source microwave power, ion source gas flow,beam extraction voltage, accelerator voltage, focus solenoid current,steering magnet current, and gas target pressure. This full system isgenerally too complex to directly model or predict a priori.Additionally, small differences between individual instances of thesystem, for example the alignment of the beamline, can have largeeffects on system performance and are difficult to incorporate intopredictive models. As such, final system optimization normally relies onempirical results. This process generally requires a skilled andexperienced operator to obtain peak performance of the system andinvolves risk of damage to components due to operator error. Embodimentsof the present disclosure address these problems by providing automatedand partially automated processes for optimization.

An automated process for final optimization of the system providesrepeatable performance while minimizing risk of damage and eliminatingthe need for a skilled operator. In certain embodiments acceleratorsystems or sub-systems may include one or more protection/monitoringcomponents including, but not limited to, thermocouples, cameras, andvoltage and current monitors automatically assess the state of thesystem and prevent the system from operating in a state which may damagecomponents during this optimization process. FIG. 5 provides exemplaryprotection and monitoring components, including: an ion source mass flowmeter and pressure gauge; an ion source thermocouple and coolant flowmeter; a focus solenoid thermocouple, coolant flow meter, voltagemonitor, and current monitor; aperture cameras, thermocouples, andcoolant flow meters; target cameras, thermocouples, coolant flow meters,and radiation detectors; extraction and suppression pressure gauge,thermocouples, current monitors, and voltage monitors; beam diagnosticcomponents such as current monitors and emittance scanners; pressuregauges; and gas analyzers.

In certain embodiments, these monitoring components communicate with acentral computer running control software, which allow automaticadjustments to the monitored accelerator system components. For example,during this process, one or more system parameters is automaticallycontrolled and adjusted while the relevant system outputs are monitored.This allows the operational phase space of the individual system to bemapped out. Such a map allows the most stable operational points to befound over the entire range of the system. Once mapped, the controlsystem can use closed-loop PID (proportional-integral-derivative)algorithms automatically to return to these stable operating points asnecessary, and without the need for a skilled operator. One example ofthe computer implement control logic is shown in FIG. 6, which providesfeedback from monitoring components to a central computer system toprevent parts of the accelerator system from operating at conditionsthat could damage various components.

In some embodiments, the ion source sub-system is monitored withmonitoring components. Initially, prior to implementing the monitoringcomponents, each parameter such as ion source magnet position andcurrent, ion source microwave power, ion source gas flow, and extractionvoltage was manually adjusted individually while performance metricssuch as the beam current were recorded. This resulted in a limitedmapping of the operational phase space. This manual process wastime-consuming and only a small subset of the operational space could beexplored in a reasonable period. Manual methods are also prone todamaging components, especially when automated health-monitoring andinterlocking systems are not implemented. To begin to address theselimitations, algorithms (such as those in FIG. 6) were developed topost-process and mine data collected during such manual optimizationruns to map the operational phase space, as illustrated by an exampleshown in FIG. 7. This partial automation improved the efficiency andrepeatability of the process but does not allow for real-time resultswhile the system is operating. In certain embodiments, monitoringcomponents are employed to track prolonged operation at given setpointsto collect long term stability statistics can also be incorporated intothe system to quantitatively determine the most stable operationalpoints.

C. Magnet Concentration/Mounting

The precise magnetic field profile in the ion source is an importantfactor for properly coupling microwave power into the plasma, so smallphysical movements of the ion source magnets can cause large changes inthe source performance. Therefore, provided here are adjustment systemsand components to adjust and fix the location of these magnets, asrequired for testing and optimization, as well as to account for subtlevariations from system to system. One exemplary embodiment of anadjustment system for adjusting and fixing solenoid magnets thatsurround a ion source plasma chamber is shown in FIG. 8. In thisembodiment, each ion source solenoid magnet is encased in epoxy, whichis used to rigidly bond the magnet to one or more attachment components(e.g., threaded metal features). The magnets are located inside aferromagnetic enclosure that concentrates the magnetic field in the ionsource region and shields the source from any external fields. Theferromagnetic enclosure has slots along its sides, allowing for theattachment of bolts from outside the enclosure to the threaded metalfeatures of each magnet assembly. The location of each magnet along theaxis of the source axis can thus be adjusted by moving the bolts alongthe slots and fixed in place by tightening the bolts against theenclosure. Thus, provided herein are reliable and relatively low costmethods and systems for both positioning and fixing the ion sourcesolenoid magnets in place.

D. Brazing and Water Cooling

In certain embodiments, provided herein are metallic assemblies (e.g.,composed of low conductance metal) that when positioned in anaccelerator system: partially intercept the high-energy ion beam,wherein the metallic assembly comprises: i) at least one water coolingchannel, and ii) a first metal component, a second metal component, andfiller metal, wherein said filler metal attaches said first metalcomponent to said second metal component at a joint (e.g., a brazedjoint).

In configurations (e.g., with a gaseous target) large pressuredifferentials across the vacuum system are maintained by low-conductancemetallic apertures that limit the flow of gas from the target to thebeamline. The high-energy ions in the edge region of the ion beamdeposit large amounts of energy on the aperture, which can lead toexcessive heating and permanent damage.

FIG. 9A shows an exemplary differential tube assembly, with parts thatare brazed together. FIG. 9A shows the following parts: a differentialtube plate (1); a first differential tube (2); a second differentialtube (3); a turbo shadow (4); an aperture tube cap (5); a pair ofaperture tube rods (6); and a plurality of plate plugs (7). FIG. 9Bshows a see-through view of an exemplary differential tube plate,showing water channels located therein. FIG. 9C shows a perspective viewof an exemplary differential tube plate.

Work conducted during development of embodiments disclosed hereinidentified water cooling as an efficient way to remove heat frommetallic parts that may partially intercept the beam. Due to the beam'shigh power density and the vacuum environment that the beam and thesecomponents are in, special considerations must be taken into accountwhen implementing the water cooling.

The reliability of the system has been found to significantly improve byusing highly thermally conductive metals (e.g., copper, aluminum) tofabricate components that may be impacted by the beam, and by addingwater cooling channels to these parts to prevent them from melting.These components often need to have complex shapes and highly thermallyconductive materials are difficult to weld, so brazing has beendetermined to be the best method to join pieces together while leavingspaces for the water to flow in. This not only allows the water channelshape to be complex and reach all the important areas, but also createsa strong, full penetration joint that maintains the high thermalconductivity of the base metal. While more expensive than some othertechniques, it provides high reliability against water leaks, which arevery problematic for water-cooled parts that are in a vacuum.

In it is noted that initially, in work conducted during development ofembodiments described herein, these components were made out of copper,tungsten, aluminum or stainless steel, but without cooling, so they didnot survive for long periods, even though they only intercepted the edgeof the beam. Water cooling channels were later added and were sealedwith NPT plugs, but the temperatures were high enough to decomposepolymers, so that the thread sealant was not effective at preventingleaks into a high-vacuum environment. O-rings have similar issues withelevated temperatures. Brazing metal plugs into position (e.g., to fillthe holes drilled to create water channels), is a superior solution. Incertain embodiments, rather than, or in addition to water channels, heatpipes are employed to remove waste heat. In particular embodiments, theoverall accelerator system's reliability is improved by using brazedassemblies with water cooling channels, as there may be fewer leakswhich can damage other expensive equipment, such as vacuum pumps.

II. Ion Source Infrastructure

In certain embodiments, the ion source infrastructure has a number ofimprovements that contribute to its improved behavior. These include,for example: the implementation of vacuum pumping at high voltage;nesting pressure vessels for operation of certain components at highvoltage; and the use of a V-belt for power transmission to components athigh voltage. Each of these improvements will be discussed in turn.

A. Vacuum Pumping at High Voltage

A fraction of the gas fed into the plasma chamber is not ionized by themicrowaves and drifts into the extraction and acceleration regions wherestrong electric fields are applied. The presence of neutral gas usuallyincreases the likelihood of high-voltage arcs, which can disrupt theoperation of the system, triggering fault states in the high-voltagepower supplies and degrading the lifetime of beamline components.Furthermore, ions in the beam can undergo atomic and molecular processeswith the background neutral gas, such as scattering or charge exchangeevents, which deteriorate the beam quality or reduce the ion current.

In light of these issues, provided herein are systems and methods thatallow removal of the non-ionized gas from the extraction region. Incertain embodiments, the ion source region is designed to allow formounting a first vacuum pump (e.g., small turbomolecular vacuum pump)directly on the ion source, inside the high-voltage dome, to remove gasentering the extraction region from the plasma source. However, theexhaust from the vacuum pump cannot be released into the high-pressure,insulating-gas-filled enclosure in which the ion source resides. Inorder to solve this secondary problem, the vacuum pump exhaust iscompressed to higher pressure with a second vacuum pump (e.g., smallroughing pump), and then passed into an insulating hose that is runbetween the high-voltage end and ground. In certain embodiments, theinsulating hose is wound in a helix shape to increase its voltagebreakdown rating. At the ground end, the gas is released to theatmosphere like a regular vacuum pump system. Pumping the exhaust gasacross high voltage is uncommon and the solution is counter-intuitivedue to the difficulty of implementation, but it permits the removal ofgas from the extraction and acceleration regions when using aninsulating-gas-filled enclosure. Pumping directly on the ion sourceregion removes most of the leakage gas from the plasma source, reducingthe pressure in the extraction region. This increases the maximumvoltage that can be used, reduces arcs, increases long-term reliabilityand allows for better beam quality. It also permits the ion sourceregion to be designed without regard to gas flow requirements,increasing design flexibility.

It is noted that prior art designs used vacuum pumps at the ground endof the accelerator, but the gas is injected at the ion source end, whichis usually held at high voltage. In that configuration, the ion sourceand accelerator had to be carefully designed to have high gas flow topermit the gas to escape down the accelerator. Even with such design,the basic physics of the system limits the vacuum level achievable inthe ion source region, limiting the maximum voltages that can be usedand increasing arc frequency, which is detrimental to stability andlong-term operation.

B. Pressure Vessel within a Pressure Vessel

Equipment that needs to be held at high voltage is usually enclosed in asmoothly shaped high-voltage dome inside an insulating-gas-filledpressure vessel, in order to minimize disruptive and potentiallydamaging arcing events. However, some auxiliary components cannotoperate correctly in a pressurized environment. Therefore, providedherein is a solution where the components (e.g., roughing pump) thatneed be located inside the pressure vessel for reliable operation athigh voltage, but cannot operate in a high-pressure environment, areplaced in a smaller (inner) pressure vessel that is pressurized tonominal atmospheric pressure, and is connected via a tube to theexterior of the larger (outer) pressure vessel.

For example, as described in the section above, a roughing pump is usedto back the turbomolecular pump added to the ion source for removing gasfrom the extraction region. The roughing pump performs best atatmospheric pressure, not the pressurized environment created by thelarger (outer) pressure pump (see, SF₆ pressure vessel in FIG. 1). Assuch, as shown in FIG. 10, a nested pressure vessel configuration isprovided, where the roughing pump is located inside an inner (smaller)pressure vessel inside an outer (larger) pressure vessel, so that it canoperate at a different pressure (e.g., atmospheric pressure). It isnoted that, in work conducted during the development of embodiments ofthe present disclosure, attempts to operate the roughing pump in apressurized environment lead to gas leaking into the pump, so that thepump had to work harder. Also, without the use of the roughing pump inthe inner pressure vessel, this could lead to gas backstreaming throughthe turbomolecular pump and poisoning the vacuum system.

C. V-Belt

Power for components held at high voltage needs to be supplied in amanner that is electrically isolated from ground. Prior art forproviding this energy has included isolation transformers and generatorsdriven by insulated shafts or belts. Most belts in production for powertransfer applications have either steel cables embedded in them, highamounts of carbon added to the polymer, or both. Both of these featuresprevent them from maintaining the voltage isolation requirement becausethey make the belt an effective electrical conductor. While other beltsdo not conduct electricity easily, they are usually either too weak tohandle the large amount of transmitted power or have been observed tobecome more conductive over time, leading to breakdown and failure ofthe belt.

A solution this problem is provided herein by providing systemscomprising: a) at least one high voltage component that is held at highvoltage in an accelerator system that generates a high-energy ion beam,and b) an electrical power component that is electrically linked to theat least one high voltage component, wherein the electrical powercomponent provides electrical power to the at least high voltagecomponent (e.g., in a manner that is electrically isolated from ground),wherein the electrical power component comprises a V-belt, and whereinthe V-belt comprises a plurality of segments (e.g., 3 . . . 25 . . . 100. . . 400 segments) and is: i) a poor electrical conductor, or ii) anelectrical non-conductor.

V-belts have been identified that can both handle the power loads thatare transferred and maintain the necessary electrical isolation. Forexample, a segmented-type V-belt such as the Fenner POWERTWIST was foundto successfully transmit large amounts of power across the voltage gap.

III. High Voltage Systems

In various embodiments, the high voltage system has a number ofimprovements that contribute to its improved behavior. These include:direct ion injection; actively-cooled water resistors; an idealelectrostatic lens design process; the use of precision insulating ballsfor electrical isolation and alignment of electron suppression elements.Each of these improvements will be discussed in turn.

A. Direct Ion Injection

Many beamlines require components located between the ion source and theaccelerator. This Low Energy Beam Transport (LEBT) section accepts thebeam as it exits the plasma source and delivers it to the acceleratorwith the required beam parameters. Typically, the LEBT includes but isnot limited to analyzing magnets, focusing elements, electronsuppression elements, and beam choppers. Such components are necessaryif the beam extracted from the plasma source is not of high enoughquality to be accepted by the accelerator. Such LEBT components add tothe size, cost, and complexity of the system. Increased complexitygenerally leads to lower reliability and a less robust system.Additionally, due to increased space charge in the beam, these problemsgenerally become more pronounced for high-current DC beamlines.

In light of these possible issues with LEBT components, in someembodiments, provided herein are direct-ion injection systems that donot employ any LEBT components. In order to provide for just direction-injection, various solutions are employed, including quicklymodulating the microwave power, altering the drift length (distancebetween ion source and entrance to accelerate column), reducing thepressure in the accelerator column, and reducing the pressure in thehigh-voltage area (e.g., using the first and second vacuum pumpsdescribed above and herein).

The high atomic fraction characteristic of microwave ion sources caneliminate the need for species-analyzing magnets between the ion sourceand accelerator. Sufficient vacuum pumping in the beamline reducesbackground ionization and the need for electrostatic electronsuppression between the ion source and accelerator. This is furtherfacilitated by adding pumping at the high voltage end of theaccelerator, as explained herein.

Many ion source technologies, such as those based on filaments, rely onthermal processes and are relatively slow to turn on and off. With suchsources, the extraction or acceleration high voltage power supplies mustbe shunted or switched to quickly modulate the beam. This addscomplexity and cost while generally reducing reliability.

In certain embodiments, the microwave ion source is directly modulatedquickly by controlling the driving microwave power. This allows the beamto be rapidly pulsed or extinguished while the extraction andacceleration high voltage power supplies remain steady. Suchfunctionality allows for system commissioning and machine protectionwithout the need for beam choppers, kickers, or high voltage switchingcircuits. FIG. 11 shows an example of pulsed beam from modulatingmagnetron (measured with Faraday Cup), which modulates the microwavesentering the plasma chamber.

In the direct injection architecture, the beam extracted from the ionsource immediately enters the accelerator, as illustrated in 12A. Thisgeometry minimizes drift length and thus reduces the increase in beamdiameter due to space charge. The ion beam diameter is an importantfactor for solenoid focusing elements. The ability to control the beamdiameter and divergence by altering the drift length between the ionsource and the accelerator thus allows for better performance whendesigning the full beamline by matching the ion source, accelerator,focusing elements, and target. Therefore, in certain embodiments, thedrift length is altered (lengthened or shortened) to optimize the directinjection architecture.

The “drift length” is the physical distance the beam travels in a regionwith no external electromagnetic fields. This corresponds to thephysical distance between the extraction/suppression/exit lens group andthe entrance of the accelerator column in the main system figure. Thisis the same location where LEBTs would be used in a non-direct injectionsystem.

Examples of drift length before the accelerator is shown in FIG. 12Bfrom 20-500 mm. In the field-free drift region, the beam becomes largelyneutralized by background free electrons and space charge effects aresignificantly reduced. Under these conditions, the envelope of the beamextracted from the ion source can be approximated as a cone with aconstant apex angle. As such, the diameter of the beam entering theaccelerator, at the end of the drift region, can be determined by thelength of the drift region in conjunction with this angle of expansion.The spherical aberrations and space charge effects in the acceleratorare dependent on the diameter of the beam, making the length of thedrift region between the ion source and the accelerator an importantfactor in the system's performance.

In is noted that, to operate reliably, direct injection systemsgenerally require a more finely tuned ion source, which typicallyrequires a lengthy commissioning process by skilled operators. Asexplained herein, automated system-tuning algorithms increase the speedand reliability of such processes. Any failures can also generally behandled automatically without operator intervention by the automatedrecovery systems explained herein. This can effectively minimize oreliminate any damage or down time caused by such transient events.

The elimination of electron-suppression components between the ionsource and accelerator column generally allows any electrons created inthe accelerator due to interactions with background neutrals or theaccelerator walls to be carried back into the ion source at high energy.This can result in damage to the ion source components, reducing theirlifetime, and puts an unnecessary load on the high voltage powersupplies, increasing their cost.

In a well optimized system, there will be negligible levels of beamcurrent impinging on any accelerator surfaces. Most of the detrimentalbackstreaming electrons are therefore created by interactions withbackground neutrals, so reducing the pressure (as discussed above) inthe accelerator minimizes these issues. As explained in detail herein,increasing the vacuum pumping capability in the high-voltage region ofsystems with electrostatic suppression lenses (described further below)between the ion source and accelerator has been found to be an effectivemethod to decrease the background pressure and thus reduce thebackstreaming electron current, while improving system reliability andstability. Adding similar pumping to the high-voltage end of a directinjection system, in certain embodiments, should further improve overallstability and increase the lifetime of accelerator components. Thedetrimental effects of backstreaming electrons which do reach the ionsource can be further mitigated with the so-called inverted waveguidediscussed in detail herein.

Implementing direction injection, such as with using the technologydiscussed above, can reduce beam diameter and improve beam transport forhigh current ion beams. Tuning the beam characteristics can allow forsmaller apertures on differential pumping systems, longer beam transportdistances, or better acceptance into downstream high-energyaccelerators. In general, smaller beam size and apertures is importantfor gas targets. Also, longer transport is important for targets whichneed to be located a large distance from the ion source including butnot limited to accelerator driven subcritical assemblies. Also,acceptance into downstream accelerators important to high energy physicslabs.

B. Actively Cooled Water Resistor

High-voltage power supplies (HVPS) are used run components ofaccelerator systems. When testing such a HVPS, it is necessary toconnect the output to a test load to ensure the HVPS meetsspecifications. The test load needs to withstand voltages of up to 300kV DC and reject up to 30 kW, or about 3 kW, or about 5 kW, of heat.Building such a test load requires purchasing multiple expensive,specialized resistors to operate at different loads.

Also, certain accelerator use a resistor divider, composed of a stringof resistors to evenly divide the voltage along the accelerator toprevent arcing and give a uniform electric field to properly acceleratethe ion beam. Conventional resistors must be rated for high voltage, arebulky, and have limited power dissipation, which limits the performanceof the accelerator.

Provided herein are, in certain embodiments, recirculating, high-power,high-voltage water resistor, or test load, which has been used to testHVPS at voltages of up to 300 kV and at power levels of up to 30 kW. Thesame concept has also been used as a flexible high-voltage gradingresistor for electrostatic accelerators (see, FIG. 13).

These systems and methods use recirculating controlled conductivitywater as the resistive element. Insulating tubing (e.g., plastic tubing)is connected between the ground electrode and the high-voltageelectrode(s). A water pump takes water from a reservoir and circulatesit through the electrodes, through a heat exchanger to remove dissipatedheat, and back to the reservoir.

Deionizing (DI) resins are used to reduce the conductivity of the water,and dilute metal salt solutions are used to increase the conductivity asneeded. By actively controlling the conductivity of the water, theresistance can be changed over a wide range. The DI resin used isgenerally capable of producing deionized water to 15 Megohm-cmresistivity or higher. This resin is often provided commercially as“mixed-bed” resin, which is composed of equal parts hydrogen form strongacid cation resin and hydroxide form strong base anion resin.

The voltage rating of the water resistor can be changed by adjusting thelength of the insulating tubes to increase or decrease the breakdownvoltage, as desired. The power capacity of the resistor is adjusted bychoosing the diameter of the tubing and the water flow rate so the waterdoes not exceed the boiling point at the design power rating.

During development of embodiments of the present disclosure, it wasfound that soft vinyl tubing developed pinhole leaks due to high-voltagearcs. Suitable materials for the electrically non-conductive tubinginclude, but are not limited to, polycarbonate, polymethyl methacrylate(PMMA), and polyethylene. Metal salts that may be used include, but arenot limited to, copper sulfate, sodium chloride, ammonium chloride,magnesium sulfate, sodium thiosulfate.

An exemplary embodiment of these systems is as follows. The waterresistor is initially charged with deionized water. For this reason, thematerials used in construction of the water resistor should becompatible with DI water systems. In general for best performance, allmetal in the system should be the same, and it may be, for example,either copper, aluminum, or stainless steel. In general, mixing metaltypes enhances corrosion and shortens the lifetime of components. Themetal salts used to decrease resistance should be compatible with themetal selected, e.g. copper sulfate is used with copper, ammoniumchloride is used with stainless, etc. A mixed-bed DI resin of 15 or 18MΩ-cm is used to remove excess ions from solution and increase theresistance. In certain embodiments, the following are employed:stainless electrodes, a stainless heat exchanger, magnesium sulfatesalt, and 15 MΩ-cm color-changing DI resin.

In a working exemplary application for a high power, high voltage load,the system is as follows. The insulating tubing was two pieces ofpolycarbonate tubing, 0.95 cm ID, 90.0 cm length. The DI resin wasResinTech MBD-30 indicating resin. Copper tubes were used to makeelectrical connection to the dilute salt solution. The electrolyte wascopper sulfate. The resistance of the test load is calculated asR=rho*L/A, where rho is the resistivity, L is the tube length, and A isthe tube area. With pure DI water of 18 Megohm-cm resistivity, the testload resistance was R=18e6 ohm-cm*2*90 cm/0.71 sq. cm.=4.6e9 ohms. Thishigh resistance is essentially zero load and permitted full voltage,zero load tests to be conducted. Copper sulfate was then added todecrease the resistivity to 2960 ohm-cm, which gave a resistance of 750kilohms. This permitted the test load to be operated at 150 kV, 200 mA.The 30 kW of dissipated power was rejected to cooling water through aheat exchanger.

In certain embodiments, PLC/software controls fully automate the system,allowing an operator to select a resistance and the system wouldautomatically compensate for small drifts in temperature orconductivity. Additionally, a sealed system or other method to preventatmospheric oxygen or CO₂ from contacting the water would increasechemical stability and prolong the lifetime of the system by requiringfewer consumables or increasing the time between service intervals.

C. Lens Design

An electrostatic lens stack is used to extract ions from the microwaveplasma source and form them into a beam. An electrostatic lens stack iscomposed of: i) a plasma lens, ii) an extraction lens, iii) asuppression lens, and iv) an exit lens. The precise shape of the lensesaffects the beam properties at given source parameters and appliedvoltages, in terms of current density, spot size, divergence andemittance. These affect the robustness of the system, the totalextracted current and the high-voltage requirements. A process isrequired to determine the appropriate lens shapes to obtain beams of thedesired properties as it propagates through downstream components (e.g.,an accelerator column, a focusing solenoid or low-conductance apertures)subject to operational constraints, such as maximum applied voltages andelectric fields.

In certain embodiments, provided herein, the lens design process startswith an internal computer code that determines nominally ideal profilesfor the plasma and extraction lenses, given the desired beam properties.It also generates a file to input the calculated lens geometry intoPBGUNS (Particle Beam GUN Simulations), a commercially available programused to simulate the ion beam transport through the extraction systemand downstream components. FIG. 14 shows an exemplary user interface forthe lens design software application.

PBGUNS outputs beam trajectories and results, can be used to confirm thesuitability of the lens stack designed, or suggest changes that can bemade to the geometry to optimize the beam quality and thus the overallsystem's performance. FIG. 15 shows a sample beam trajectory plot fromPBGUNS.

The inputs to the lens shape determination code are: beam current,extraction voltage, ion species fractions, maximum electric field, andion current density at the plasma lens aperture. The code outputs lensesthat result in spherically convergent, space-charge-limited ion flowbetween the plasma and extraction lenses, while satisfying the equationsfor zero charge (Laplace equation) outside the beam and yielding amatching solution between the two regions, at the edge of the beam.

PBGUNS has many inputs beyond the geometry of the system. These includethe grid precision, an empirically determined beam neutralizationfactor, and the electron and ion temperatures in the source plasma. Theprogram outputs a beam trajectory plot, as well as phase space plots andemittance calculations at specific axial locations. Some limited beamletdata is also output for a single axial location per run, which can beused for post-processing the results in greater detail.

In certain embodiments, other programs are used to design lenses thatallow for simulating 3D configurations (e.g., if one considersmultiple-aperture extraction systems to increase the total current thatcan be extracted from a plasma source, which may be important for someapplications). Other software packages such as IBSIMU allow for 3Dconfigurations, while also running 2D geometries faster than PBGUNS,though the full calculation may not be as accurate.

D. Implementation of Suppression Elements

High energy ion beam generators may employ an extraction lens stack,with a suppression electrode biased negatively with respect to theextraction lens and located immediately downstream from it, followed byan exit electrode in electrical contact with the extraction lens. Theresulting dip in the electrostatic potential prevents electrons createddownstream (e.g., by ionization or secondary emission off solidsurfaces) from being accelerated to high energies and damaging sourcecomponents. The confined electrons can also contribute more effectivelyto the space-charge compensation of the ion beam, reducing the beamsize, divergence and emittance. Such a lens stack thus enhances thereliability of the system, improves the beam quality and increases thetotal current that can be transported to the target, resulting ingreater uptime and throughput.

Provided herein are components used to align and hold together theelectrodes in the lens stack, while withstanding the high voltagesbetween them. This mechanism is mechanically robust, provides electricalinsulation, is compatible with ultra-high vacuum, and is rated foroperation at high temperatures, a complex set of criteria to balance.

In some embodiments, insulating balls (e.g., ceramic balls) are pressedbetween conical indentations on each pair of electrodes stackedtogether, for example, as shown in FIG. 16. In some embodiments, foreach lens gap, three insulating balls (e.g., ceramic balls) are spacedevenly in the azimuthal coordinate to achieve mechanical contact on afully defined plane. Given their high degree of spherical symmetry anddiameter tolerances, ceramic balls allow for self-alignment of thelenses, since two electrodes pressed firmly against opposite sides ofthree ceramic balls have no remaining degrees of freedom, compared toother geometries.

Ceramic balls are rated for ultra-high vacuum, very high temperatures,are very hard and rigid, and have a high dielectric strength, providinginsulation for use at high voltages. In some embodiments, the whole lensstack is held together by metallic bolts between the extraction and exitelectrodes since these are held at the same electrostatic potential andelectrical contact between them is desired. Metallic bolts are also muchmore durable than ceramic bolts.

Ceramic balls are readily manufactured or are available as off-the-shelfcomponents, with very high precision in diameter (−0.1%) and sphericity(−0.01%) and at a relatively low cost. Ceramic balls are often made outof mostly alumina and are rated for temperatures over 1000° C., althoughother materials may be employed.

Before using precision ceramic balls, ceramic bolts, nuts and washerswere used. These can be rated for vacuum, high temperatures andhigh-voltage operation. However, they are brittle and can break easily,as they are susceptible to shear stresses, especially when the axis ofthe lens stack is oriented horizontally. Also, since the through-holesin the electrodes are necessarily larger than the major diameter of thebolt threads, the lenses have a minimum of two degrees of freedom, sothat self-alignment was not a feature of that type of assembly.

The use of precision ceramic balls has allowed for mechanically robustassembly of the extraction lens stack using a suppression electrode,plus inherent self-alignment between the lenses, while allowing for useat high voltages, high temperatures and ultra-high vacuum. Thiscomponent helps improve the reliability of the overall system, in termsof mechanical stability, beam quality, and protection of source andbeamline components, while increasing the total current that can bereliably transported to the target of interest.

IV. Neutron-Producing Target

A number of advances have been made to the neutron-producing targetsystem that contributes to is exemplary performance. These include: A)the active cooling mechanism for a solid target; B) an argon sputtercleaning process; C) a mechanism for distributing the thermal load ontube apertures in a gaseous-target system; D) a reverse gas jet; and E)the implementation of a beam scraper.

A. High-Power-Density Solid-Target Cooling

For accelerator-driven neutron generator systems, the majority of theion beam energy results in target heating rather than nuclear reactions.High-yield systems necessarily require high-power ion beams and removalof the resulting large heat loads produced in the target.

Solid targets are composed of a reactive species, typically deuterium ortritium, embedded in a solid matrix of non-reactive material. Such anon-reactive matrix generally will further reduce the efficiency of thegenerator as any interactions with the ion beam will only result inwaste heat and not any desired nuclear reactions. Additionally, the highdensity of a solid target generally leads to a short stopping distancefor the incident ion beam resulting in a high volumetric power densitydeposited into the target.

The volume in which the desired neutrons are produced through fusionreactions is defined by the volume within the target into which the beamions are deposited. For certain applications, including but not limitedto fast neutron radiography, a point-like neutron source is desirable toprovide higher quality images. This corresponds to a small ion beam spotsize on the target.

For a given total neutron yield, measured by the number of neutronsproduced in a period of time, the neutron flux, measured by the numberof neutrons per time per area, is generally increased as theneutron-producing volume within the target is reduced. A high neutronflux is desirable for applications including but not limited to neutronactivation analysis and materials testing for reactor components.

For reasons including but not limited to those described above,depositing the ion beam's energy into a small volume is desirable forthe performance of accelerator driven neutron generators. Beam-focusingelements can be used to reduce the spot size on the target to nearlyarbitrarily small areas limited by space charge effects. In practice,the achievable spot size is limited by the high power deposition of theion beam into the solid target.

For the application of accelerator-driven neutron production via fusionreactions between nuclei of hydrogen isotopes, a solid target materialwith a high hydrogen storage capacity such as titanium is desirable forhigh neutron yields. Deuterium or tritium is embedded into the targetdirectly by the beam in situ or in an oven baking process.

Beyond the physical destruction of a solid target through mechanismsincluding melting and ablation, solid-target neutron generatorsutilizing deuterium or tritium nuclear reactions must be maintainedbelow the temperature at which diffusion leads to loss of hydrogen fromwithin the target material. Generally, the hydrogen vapor pressure ofmetal hydrides becomes prohibitive at temperatures above about 250degrees Celsius.

In general, there are two fundamental cooling requirements for the ionbeam target. First, the total average power deposited by the beam shouldbe rejected to prevent the bulk heating of the target assembly over timescales on the order of the thermal time constant. Second, theinstantaneous power density of the beam incident on the target materialshould be low enough to prevent immediate localized material damage.

The average ion beam power is determined by the product of the beamcurrent, beam energy, and duty cycle. This value is typically on theorder of thousands to tens of thousands of watts in some of theexemplary systems described herein, though the same principles apply tohigher power levels. The resultant steady state bulk temperature rise isdetermined by the mass flow rate and specific heat of the coolant. Thisfirst requirement is readily satisfied with modest mass flow rates(e.g., 10-100 gallons/minute of coolant) of coolants including but notlimited to water, glycol, or oil.

The second requirement, relating to volumetric power density, isgenerally more difficult to achieve for high performance systems. Theincident beam power is deposited into a thin surface volume defined bythe beam spot size and the stopping power of the beam in the target.This power must transfer through the target material and into thecoolant before being removed. Heat transfer at an interface is definedin part by the materials, geometry, surface condition, and coolant fluiddynamics.

The target temperature should be kept below about 250 degrees Celsius toprevent loss of embedded hydrogen and hydrides required for nuclearfusion reactions. This is accomplished with minimized target wallthickness, high thermal conductivity materials, increased coolantsurface area, turbulent coolant flow, and clean coolant channelsurfaces.

The performance of early systems using open-loop water cooling was foundto degrade over time. Given the very low thermal conductivity of mineraldeposits that build up in the cooling channels, even an extremely thinlayer has a significant effect on heat transfer and on the resultingtarget surface temperature. The elevated temperatures inherent in thetarget tend to increase the precipitation of mineral deposits, whichrestrict coolant flow, reduce cooling capacity, and can create runawayfailure modes.

Closed-loop cooling with actively filtered and deionized coolantprevents such deposits in the target while extending the lifetime andimproving the performance of the target.

One approach to reduce the power density on the solid target is toposition it on an oblique angle such that the ion beam is deposited overan ellipse with a high eccentricity and increased surface area. Manytargets utilizing single angled planes, arrays of angled planes, orcones were tested. Such geometries are used on high-power beam stopswhere neutron production is not the primary application. Targets usingthis method are necessarily larger, more expensive and complex, andgenerally require more ancillary hardware. This makes such an approachundesirable for systems requiring a point-like neutron source or acompact and easily portable system.

To reduce the target size, the beam spot size on the target must bereduced resulting in higher power densities. To maintain the targetsurface temperature requirements under these conditions, more efficientheat transfer is needed. In some embodiments, the target walls are ofminimal thickness (e.g., 0.005 to 0.020 inch; e.g., 0.010 inch). Thisdimension is limited by the structural integrity necessary to containthe coolant channel pressure. The difference in temperature between thetarget surface intercepting the beam's power and the coolant isproportional to the thickness of the target wall and the wall material'sthermal conductivity. As such, both the material and physical structureof the target and cooling channel walls determine the performance of thesolid target. Reducing the target wall thickness therefore allows forlower target surface temperatures. The ideal wall material has a highthermal conductivity, high tensile strength, and high machinability.Such materials include but are not limited to copper, silver, gold,diamond, diamond like carbon, or a combination thereof.

Additionally, the effective surface area is increased through theaddition of fins, ribs, or other convolutions. Such features canincrease the structural strength of the target allowing for thinnerwalls. Features can be manufactured with multiple techniques includingbut not limited to milling, casting, or additive manufacture. Example ofturbulence inducing structures include a plurality of parallel fins withdimpled holes to interrupt smooth surfaces. An exemplary structure isshown in FIG. 17.

In the some embodiments, water is used as the coolant. This allows useof a wide range of low cost and reliable commercial pumps, filters, andother ancillary equipment to support the cooling system.

Other embodiments may make use of other coolants including but notlimited to oils, gasses, or liquid metals. Additives may also be used toalter the properties of the coolant.

A high quality closed loop coolant system maintains clean coolantchannel surfaces. This sealed system prevents atmospheric oxygen orother substances from being available to react with the surfaces of thecoolant channels. The coolant loop is also further processed withtechniques including but not limited to deionization and filtering.

Laminar flow produces an insulating layer at the fluid-solid interfaceof the cooling channels and restricts heat transfer. Irregular featuressuch as intermittent dimples and spiraled indentations, as illustratedin FIG. 18, tend to induce turbulent flow instead, improving the heattransfer of the system. The fluid coolant channels are located withinthe fact of the solid target assembly. This assembly is located at theend of the beamline. In the some embodiments, the solid target islocated at ground potential and does not require any specializedconnections to the overall system. In some embodiments, the solid targetis thermally isolated from the rest of the system. This allowscalorimetric measurements of the power deposited by the ion beam intothe target by monitoring the temperature and flow rate of the coolantthrough the target. As the energy of the ion beam is known, the powerdeposited can be used to determine the electrical current carried by theion beam to the target.

Other embodiments of the solid target assembly are electrically isolatedfrom the overall system allowing it to be biased to a high voltage inorder to increase the effective ion beam energy and neutron yield. Suchembodiments entail the coolant be transported to the high voltage solidtarget from pumps located at ground potential or use of a fully closedloop cooling system isolated at high voltage. Such methods are similarto those described herein for providing cooling or electrical power tothe ion source which is also electrically biased to a high voltage withrespect to earth ground.

Turbulent flow also generally has larger pressure losses. The coolantflow rate and pressure drop should be considered in the design of theturbulence-inducing features. Computational fluid dynamics simulationsare used to determine these values and match them to the performance ofthe coolant pumping system. By adjusting the number of elements inparallel or in series, the operational flow rate and pressure drop ofthe target is adjusted.

The heat transfer performance of the target is characterized by atemperature differential between the coolant and the target surface. Theabsolute temperature of the surface is therefore reduced for a givensystem by reducing the inlet coolant temperature. Pre-cooling of theclosed loop coolant is achieved with a chiller or other methods. Thelowest achievable coolant temperature is generally limited by themelting point of the coolant.

The pre-cooling of water-based coolants is limited by its relativelyhigh melting point. The use of other coolants, such as helium, allowsfor much lower temperatures of the coolant as it enters the target. Thisresults in a lower target surface temperature for a given ion beam powerdensity. Similarly, higher ion beam power densities, resulting in morepoint-like neutron sources and higher fluxes, can be achieved whilemaintaining the necessary low target surface temperature.

The low mass of hydrogen species results in a low sputtering rate formetal targets. The lifetime of the target surface is reduced if the beamcontains heavier ion contaminants, which can be removed with ananalyzing magnet or other mass-filtering component in the beamline priorto the target.

High-power-density ion beam targets allow for more physically compactand portable systems, more point-like neutron sources, and higherneutron fluxes.

B. Cleaning of Solid Target to Maintain Neutron Yield

Neutron sources sometimes use a beam target plated with titanium metal.The titanium adsorbs significant amounts of deuterium so that incomingdeuterium can cause fusion reactions, releasing neutrons. However,titanium is a fairly active metal that can also react with oxygen andnitrogen, forming a barrier to the deuterium beam and lowering neutronoutput. Trace contaminants in a vacuum system can be high enough tocause this problem to occur.

In some embodiments, a small amount of argon gas (e.g., 1 to 10 standardcubic centimeters per minute) is flowed into the vacuum system while thebeam is operational. The ion beam transfers some kinetic energy to theargon gas. The energetic argon atoms then impact the target surface andremove the contaminating oxide/nitride layer by sputtering. Argon ismuch heavier than the primary beam species, so it is efficient forinducing sputtering, while its chemical inertness prevents it fromforming other compounds with titanium on the target surface. FIG. 19shows the effects of titanium compound formation and the argon cleaningprocess on the neutron yield. The target initially loads with deuteriumup to 10,000 seconds, but then a slow accumulation of titaniumoxide/nitride lowers the neutron output. A brief argon cleaning occursat 125,000 seconds and an extended cleaning between 150,000 to 175,000seconds, bringing the neutron output back up to initial levels.

The argon should be fed into the vacuum system as close as possible tothe solid target in order to make the local argon pressure near thetarget as high as possible without excessively increasing the overallvacuum system pressure. In some embodiments, a source of argon gas isconnected to the vacuum system by a metal tube that resides inside thevacuum and delivers the argon directly at the solid target location.

Other heavy, inert gasses may also be employed, such as krypton andxenon, although they are more cost prohibitive.

The only previous method was to remove the target from the system andmechanically clean the target to remove the titanium oxide/nitridelayer. This was a time-consuming process and removed significantly moreof the target plating than necessary, severely reducing target lifetime.Furthermore, periodic replacement of targets reduces the uptime of thesystem, and thus the total throughput for the user over time.

C. Tube Apertures

In gaseous-target neutron generators, a large pressure gradient needs tobe maintained between the target and the accelerator in order tomaximize the total neutron yield. Therefore, the aperture separating thetarget gas from the ion beam accelerator is necessarily small (e.g., afew millimeters in diameter). The ion beam power density iscorrespondingly large when passing through the aperture (hundreds ofMW/m²) and is not tolerable by any solid surface in steady-stateoperation. Small deviations in beam focus and steering due tothermal/mechanical or electrical variations in the accelerator systemcan result in severe damage to the target entrance aperture. This canlead to degraded system performance if the pressure gradient cannot bemaintained or even severe system damage due to loss of vacuum and/orcooling water entering the vacuum system.

The ion beam is a few centimeters in diameter as it exits theaccelerating stage and must be focused down to a few millimeters inorder to pass through the entrance aperture to the gaseous target. Theaxial distance at which the beam is focused to its smallest diameter isdependent on the current in the focusing solenoid. A variety of anadjustable focusing mechanism may also be used, including electrostaticor magnetic quadrupole multiplets or permanent magnet/electromagnethybrids.

In some embodiments, the ion beam is deflected laterally in twoorthogonal directions by varying the currents in a crossed pair ofdipole electromagnets (“steering” magnets) such that the central axis ofthe beam is centered on the gas target aperture, compensating for theaccumulation of angular deviations due to mechanical tolerances in thealignment of beamline components over the long beam transport distancebetween the plasma source and the gaseous target.

Provided herein are systems to sense the distribution of ion beam poweron the target aperture and use the information to actively control thefocus and steering of the ion beam through the aperture. In someembodiments, this is accomplished with a four-quadrant thermalinstrumentation embedded near the upstream-facing surface of thegaseous-target aperture, equally spaced at 90 degree intervals about theaxis of the aperture. An exemplary implementation uses copper-constantanthermocouples in a copper target aperture, which may also serve as thecopper leg of each thermocouple or the copper wires may be brought outseparately. Other embodiments use platinum resistance temperaturedetectors (RTDs), thermistors, or semiconductor temperature sensors.

The four quadrant temperature signals are summed to provide an averagetarget aperture temperature, which is used to maintain ion beam focus.Adjusting the current in the focusing solenoid to minimize thetemperature of the target aperture maintains best focus against smallperturbations due to beam voltage or current variation, or due todeflection or distortion of the overall beamline due to thermalexpansion or mechanical stress.

In this implementation, the sensors are arrayed about the axis of thebeam passing through the target aperture at the positions toward whichthe steering dipole magnets laterally deflect the beam. The temperaturedifference between a first pair of diametrically opposed temperaturesensors is used to maintain centering of the beam between the twosensors in the pair, which is also the center of the gas targetaperture. Thus the current in a first magnet may be varied to minimizethe temperature difference between a first pair of sensors correspondingto the direction that magnet deflects the ion beam. The differencebetween a second pair of diametrically opposed sensors and thecorresponding variation of current in a second steering dipole magnetmay be used to center the beam in the direction orthogonal to the firstpair of sensors. FIG. 20 shows an exemplary embodiment of this system.The top panel shows the position of the thermocouple measurement pointson the target aperture. The lower panel shows this component in thecontext of the beam and the dipole steering magnet.

D. Reverse Gas Jet

In a gaseous-target neutron generator, the pressure in the target shouldbe as high as possible, such that the beam fully stops in as small adistance as possible, and the pressure just before the target should beas low as possible, such that energy is not wasted creating neutrons inan area where they cannot be effectively used.

Provided herein are components to increase the pressure differentialacross the final aperture. In particular, provided herein is a reversegas jet to effectuate the increase in pressure differential across thefinal aperture. An exemplary configuration of the reverse gas jet isshown in FIG. 21.

Modeling was done with a computational fluid dynamics (CFD) program togenerate the geometry of a nozzle that would increase the pressuredifferential across the target aperture. Initial attempts used a nozzlethat did not diverge after it converged, which did not work at all atthe pressures of interest. Aspects such as throat gap, nozzle angle,nozzle length, and pressure in the plenum were varied. The plenumpressure was always kept below atmospheric pressure, to ensure that gasleaks and gas inventory would be kept to a minimum. After significanteffort, a configuration as shown in FIG. 21 was developed and providesthe desired pressure differential.

The aperture that the gas jet nozzle sits around was chosen to be ⅜″(although other dimensions may also be employed), based on otherrequirements such as the size of the beam as it passes through theaperture. At this hole diameter, and with the types of pumps that weredesired to use to drive the gas jet, a throat gap of less than 0.01″ wasimportant to keep the pressure drop high enough to cause supersonicflow. An average nozzle angle of 12.5 degrees was found to be optimalwith parametric studies.

E. Beam Scraper

In some systems, a mechanism of inserting a solid target in the path ofthe beam that can block an arbitrary fraction of the beam is sometimesdesired for precisely controlling the total current delivered to thetarget. Such a beam scraper can also be used to determine the beamprofile, which is useful information during the optimization of theoverall system.

In some embodiments, a solid target is affixed to a rail feature, andmoved along that rail by a linear actuator made up of a long screwdriven by a motor. Software measures the position of the target alongthe rails with “home” and “limit” switches in real time, and adjusts theposition based on feedback from the system.

An initial approach used a rotary motion feedthrough that had the screwinside the vacuum. However, this required preventing galling in avacuum, where lubricant selection is difficult, as well as coupling themultiple shafts together in tight quarters. Furthermore, the vacuumchamber was much larger and more expensive.

An alternative approach was attempted with success. The motor for thelinear actuator creates heat, so it mounted outside the vacuum vessel,so that it uses air for cooling. This required the use of a linearvacuum feedthrough. Because most linear motion vacuum feedthroughs arebellows-sealed, they require a force to balance the vacuum force appliedto the bellows, and as such put more strain on the motor to overcomethose forces. Bellows-sealed feedthroughs also have a limited number ofcompression cycles they can withstand before they fail. For thesereasons, a magnetically coupled feedthrough is more desirable, since ithas neither of these problems.

Also, due to the negative consequences of water leaks in the vacuumsystem, in some embodiments all-metal hoses and fittings are used, andbrazing is used to manufacture the entire target. This ensures that noleaks are possible without the metal itself failing. The target shouldalso be designed such that no part of the target is in the path of thebeam when it is fully retracted, including rails, support structure, ortubing.

FIG. 22 provides an exemplary configuration of a beam scraper. The motorand magnetic coupling are shown outside of the vacuum boundary. Thetarget and associated water hoses are shown inside the vacuum boundary.The solid target is used on beams that are smaller than 6″ in diameter.When fully retracted, the part closest to the beam is the face of thetarget that is normally hit by the beam when it is extended, and thatedge is more than 3″ away from the centerline of the beam.

An alternative embodiment involves mounting the solid target on a hingeso that it swings into the beam path instead of linearly translating thetarget. This approach decreases the power density on target until it isfully closed, reduces the space requirements, and allows for simpler andless expensive feedthrough design. As a trade-off, the tubing might ismore difficult to implement for this configuration. This approach allowsa normally closed/open configuration, and is contemplated to have fasterclose/open times.

An alternative for systems that require an axisymmetric beam reachingthe main target involves an iris-type beam scraper.

V. Automated Control Systems

In some embodiments, the systems and methods employ one or moreautomated control components. Such automated control components include,but are not limited to, a fiber-optic interlock, a health-monitoringsystem, an automated recovery system following arcing events, and aclosed-loop control for managing beam stability.

A. Fiber-Optic Interlock

The high energy ion beam generators incorporate one or more, typicallyseveral, high-voltage sources. For safety reasons, a user/controllerstation should be electrically isolated from the rest of thedevice/system, and yet a component for connecting the user station tothe interlock system of the rest of the device/system should exist. Thiscreates a significant conflict between safety and operability.Approaches such as the use of an isolation transformer for providingelectrical isolation between the two subsystems is not technically oreconomically practical because the presence of voltages of up to severalhundred thousand volts.

An interlock is a number of normally-closed switches in series that mustremain closed to indicate that a piece of equipment is safe to operate,or a number of normally-open switches in parallel that must remain opento indicate that a piece of equipment is safe to operate, or both aseries loop and a parallel loop.

In some embodiments, the conflict between safety and operability isresolved by employing a fiber-optic connection between the device'sinterlock system and the user station's interlock. This provides theneeded electrical isolation. To provide a robust connection that isimmune to casual circumvention, in some embodiments a frequencygenerator is included in the fiber-optic interlock, as detailed below.In some embodiments, multiple-signal verification procedures are alsoimplemented in order to protect the system from producing a false-closedresult with a single-point failure.

A first attempt to address the challenge involved a fiber-optictransmitter that produced a light when the user station's interlock wasclosed. This method was not satisfactory because it did not include theuser station properly, since the user station's interlock closed signalwas not dependent on any components earlier in the interlock string.

To resolve the problems with the first implementation, a two-way linkwas installed. When the upstream interlock switches are closed, a lightis transmitted to the user station through a fiber-optic cable. Thelight is converted to a voltage signal which passes through theinterlock switches at the user station. Once the light signal from thedevice is present and the user station switches are all in the ‘safe’position, a light is transmitted back to the device thus closing theinterlock loop. The problem presented by this solution was that it wassimple to circumvent the user station interlock devices by simplyconnecting the transmitter and receiver on the device, thus closing theloop regardless of the condition of the interlock switches in the userstation.

The fiber-optic interlock signal was made frequency-dependent, in orderto make it more difficult to circumvent the interlock system. A smallfrequency generator triggers the fiber-optic transmitter, causing thelight to pulse at a set frequency. The receiver is configured to besensitive to the frequency of the light pulses it is detecting, and ifthe proper frequency is not present, the receiver does not indicate thatthe interlock is safe.

Further, in order to allow for a single device to utilize multiplefiber-optic interlocks, a printed circuit board (PCB) was configured sothat with proper tools, any one of four different frequencies can beselected. This also allows a single two-way link to use a differentfrequency for transmitting than it does for receiving, thus preservingthe obstacle to an method of circumventing the integrity of theinterlock signal.

FIG. 23 shows an exemplary block diagram for a fiber-optic interlocksystem that may be employed with the system. A fiber optic transmissionis made between a transmitter and a received via an electricallyisolated portion of an interlock circuit. The transmitter may employ aninput from a standard copper interlock. This can accommodate a singleloop with N/O (normally open) or N/C (normally closed) switches, or adouble loop with one or each type. When all interlock switches are in acorrect position, voltage reference becomes present. When voltagereference is present, voltage is scaled to a selectable level. Afrequency converter produces a frequency that is proportional to thescaled voltage. A fiber optic drive circuit pulses the fiber opticoutput to the user station at the selected frequency.

At the received side, a fiber optic receiver converts fiber optic pulseinto voltage square wave of the same frequency. In some embodiments, afrequency to voltage converter takes frequency received through thefiber optic transmission and coverts it back into the original referencevoltage. A window comparator verifies the proper frequency is beingreceived. When the comparator verifies that the received frequency iscorrect, a driver circuit closes on pair of N/O contacts and opens onepair of N/C contacts to be integrated into a local hardwired interlockloop or loops. An output to a local interlock string capable ofaccommodating an N/C loop, an N/O loop, or both is made. In someembodiments, a missing pulse detector circuit provides a secondarysource of detection when the pulse train is missing from the fiber opticsignal. When rising and falling edges are independently verified to bepresent in expected intervals, a driver circuit closes one pair of N/Ocontacts and opens one pair of N/C contracts to be integrated into alocal hardwired interlock circuitry. An output to a local interlockstring capable of accommodating an N/C loop, an N/O loop, or both ismade. In some embodiments, a second frequency to voltage converter takesfrequency received through the fiber optic transmission and coverts itback into the original reference voltage. Then a buffer stage sendsanalog signal to the controller to be used as software verification thattransmission of correct frequency is being received. This componentincreases system safety to a desired level, while remainingtechnologically and economically practical.

B. Health Monitoring

Given the high power carried by the beam, it is important to ensure thatit does not cause thermal damage to components of the system. Damage canbe caused by the beam interacting with system components in anoff-normal situation. Specific material selections and coolingmechanisms have been implemented for components that can interact withthe beam such that different protection schemes are implementeddepending on the energy density that might be deposited on eachcomponent.

In some embodiments, instrumentation and a plurality of sensors areintegrated into the system for measuring temperatures and cooling waterflow rates. These measurements allow for monitoring the amount of powerbeing deposited on various cooled system components. The combination ofthresholds for minimum flow rates, maximum temperature, and maximumpower allow for protection of the system hardware. These values arecontinuously monitored by sensors covering all components that might bedamaged by interaction with the beam. In some embodiments, each sensorhas configurable levels above or below which an alarm is tripped,causing automated control system action to intervene and ensure safeoperation and minimize or prevent damage.

In some embodiments sensors for liquid level are integrated into thesystem for measuring the presence of neutron moderator required for safeoperation. In some embodiments a combination of signals from multiplesensors are used together to determine operation within safe parameters,for example voltage draw and current to determine resistance in amagnetic coil.

In some embodiments feedback signals from components are monitored toensure operation within desired safety ranges, for example power draw onturbo molecular pumps and forced air cooling fans.

In some embodiments feedback signals from integrated components such ashigh voltage power supplies, gas flow controllers and magnetron powersupplies are monitored and their output compared to expected set valuesto determine safe operation.

In some embodiments integrated components are prevented from being setto an unsafe set-point by the control algorithm, for example preventinga user from commanding the microwave generator when the system is not ina state where the microwave can be safely operated. Another example ispreventing beam operation when any part of the system is not in a stateto safely transport or accept beam.

In some embodiments, the health monitoring system has both “Alerts” and“Alarms.” Sensors are configurable to signal an “Alert” condition if asignal deviates from a normal operating value, displaying a warningindicator to a user. A deviation that is greater in magnitude triggersan “Alarm,” resulting in automated control system response to thecondition. In some embodiments, an “Alarm” acts in a latching fashionand requires the user to reset the condition from the control system inorder to remove the alarm status.

One of the challenges encountered with health monitoring on a particleaccelerator is filtering out false positives due to short livedtransients that cause nuisance tripping of alarms. High-voltage systemsinherently create electromagnetic pulses (EMP) and thereforeelectromagnetic interference (EMI). Sensor and component data that istransmitted to the control system using analog voltage signals can besusceptible to EMI pickup. In some embodiments, the raw signal data isprocessed to filter out EMI to prevent nuisance tripping. In someembodiments, an alarm is not triggered until the duration of anindividual signal is longer than characteristic for EMI pickup. In oneexample a single transient must exceed 75 milliseconds prior to trippingan alarm. Additionally, in some embodiments, the system is configured totrip if multiple EMI pickup events occur within a certain period oftime. In one example, 5 transient events within a 3 second window oftime is considered a valid tripping of an alarm. In some embodiments,both single events lasting longer than the characteristic EMI pickup andmultiple events occurring within a certain period of time are analyzedtogether such that when either event occurs an alarm is tripped. Thiscombination of counting EMI events and tracking them over time, but nottripping an alarm on individual EMI events, allows for reliablecontinuous operation.

The automated response from the control system to an “Alarm” can be asafe shutdown or an automated recovery. A safe shutdown, for example, iswhen the control system automatically turns off the accelerator and putsthe components in a safe state. An automated recovery is, for example,when the control system takes a prescribed sequence of steps to returnthe system to normal operation.

C. Automated Recovery

Occasional “arc down” events, in which current finds a path from highvoltage points to ground through an undesired path, are not entirelypreventable in high-voltage accelerators. Preventing the system fromremaining in an undesired state following an arc down initially requireda trained user to be at the user interface to the control system andready to act at all times. This is resource intensive. Recovery from anarc down required several components to be turned off and then back onin a certain sequence with fault clearing on certain components as partof the recovery sequence.

As an extension of the health-monitoring system described in sectionV(B) above, certain “Alarm” conditions are used to indicate that an arcdown event has occurred. An automated recovery sequence is then executedto return the system to operation without user intervention and muchmore quickly than a human user. During an extended continuous run, thisfeature increased the effective uptime of the system from around 95% togreater than 98%.

In some embodiments, certain conditions are flagged in the system forautomated recovery while others are flagged for human intervention. Anexample of an automated recovery from an arc down event on the highvoltage power supply (hvps). The hvps arc down event is identified by anunder-voltage alarm on the hvps and/or the extraction power supply.Following detection of the fault condition an automated recoverysequence is executed which includes the following steps: disable closedloop feedback, disable magnetron power supply, disable extraction powersupply, clear system fault, reset hvps, enable extraction power supply,enable magnetron power supply and finally re-enable closed loop control.Any fault that has not been identified as having an automated recoverysequence triggers an automated shutdown sequence. An automated shutdownsequence includes steps to disable each component in a safe sequence. Anexample of a safe shutdown sequence includes the following steps:Disable closed loop control, disable magnetron power supply, disable allgas flow controllers and power supplies.

In some embodiments, if the recovery sequence is executed more than aconfigurable number of times within a window of time (e.g., 3 recoveryattempts within a ten second period of time) the control system executesa safe shutdown rather than the recovery sequence.

The control system for the accelerator is responsible for monitoringcomponents at high voltage, components at ground voltage, and forconnecting to a user interface for human interaction. In someembodiments, communication between the different locations is performedover fiber-optic connections in order to maintain electrical isolation.In some embodiments, the main system controller is connected directly tothe high voltage and ion source microwave power supply and can set thesecomponents deterministically to a safe state. Since there are multiplelocations of components and non-deterministic communication protocols(Ethernet, TCP/IP) between the locations, a watchdog architecture isused to monitor connectivity. In the event of the loss of connection thesystem automatically and deterministically transitions to a safe state.

Due to the non-deterministic nature of the communication protocol, someamount of missed communication is expected. At times, resetting of awatchdog may be late. In some embodiments, rules are configured based onthe frequently of the watchdog checks for connectivity and how late theresetting of the watchdog can be. This configurability reduces falsepositives where the watchdog sends the system to a safe state.

D. Closed-Loop Control for Beam Stability

Particular applications of a neutron generator require the neutron fluxoutput to be maintained within 1% peak to peak of the flux set-point,with the flux set-point being a variable over five orders of magnitude.Open loop control by a skilled operator is insufficient to ensure thatthe flux output remains within the required accuracy, due to multiplevariables affecting the system dynamics.

Closed-loop control of either the high voltage power supply (HVPS)set-point or of the beam scraper position demonstrated improved accuracyof the flux output and the ability to compensate for physical variationssuch as thermal fluctuations or target loading, and signal noise.Control of the HVPS set-point provides a faster dynamic response in themeasured flux output. Closed-loop control yielded a visible andmeasurable improvement in the stability of the neutron flux output overtime. It also reduces operator interaction with the high energy ion beamgenerator control system, which in turn reduces the potential foroperator error.

Open-loop control is used to bring the system up to the initial neutronflux setpoint, after which closed-loop control is activated. The controlgains are determined based on the selected neutron flux setpoint,ensuring closed-loop control over a smaller operating envelope. Whileclosed-loop control is active, additional limits are placed on thecontrol authority, in the form of maximum and minimum HVPS setpoints fora given neutron flux setpoint.

The physics of a neutron generator is nonlinear when considered over theentire machine operating regime, encompassing five orders of magnitudeof neutron output. The mechanics of the beam scraper, for which acircular beam impinging on a flat plate with a straight edge, whichallows a portion of the circular beam to proceed through, contributefurther to the nonlinearity of the control problem.

A linear control strategy was applied to this system by enforcingoperation over a small, linear portion of the system's operatingenvelope. Traditional control loop tuning methods can thus be applied todevelop the gains specific to each operating point. While control of theHVPS setpoint was active, the scraper position was held steady, and viceversa. This removed the nonlinearity inherent in the scraper motion fromthe control problem.

Closed-loop control of the neutron flux output via control of the beamscraper position was successful, but it did not perform as well ascontrol of the HVPS setpoint. The ability of the beam scraper positionto control flux output was dependent on the initial position of thescraper. Using a linear control algorithm to set the position, which hasa nonlinear effect on flux output, was not selected as optimal in favorof applying a linear control loop using the HVPS voltage as the controlvariable.

Further features of the control system include, but are not limited to,autotuning algorithms to accelerate development of control gains,dynamic signal analysis of the physical system, either in open or closedloop form, modeling the open-loop neutron generator system based onfirst principles, enabling state space or pole placement controlalgorithms, full system simulation to enable hardware in the loop (HIL)methods for selecting control schemes, fuzzy logic control algorithms toenable bumpless transfer between operating regimes, and generation ofprotocols to enable completely automated operation of the neutrongenerator system, including automated startup, turn off, and errorhandling.

E. Closed Loop Control for Beam Current

Particular Applications of a particle accelerator for ion implantationrequire beam current to be maintained within +/−1% of a currentsetpoint. Multiple signals are required to calculate beam currentincluding high voltage power supply source current, extraction powersupply resistor divider drain current and current losses due to leakagein the cooling water. Real-time calculation of the beam current fromthese signals is performed by the control system. Open loop control by askilled operator is insufficient to ensure that the beam current outputremains within the required accuracy, due to multiple variablesaffecting the system dynamics.

VI. Exemplary Applications

A. Thermal Neutron Radiography

Neutron radiography and tomography are proven techniques for thenondestructive testing of manufactured components in the aerospace,energy, and defense sectors. It is presently underutilized because of alack of accessible, high flux neutron sources. Just like X-rays, whenneutrons pass through an object, they provide information about theinternal structure of that object. X-rays interact weakly with lowatomic number elements (e.g. hydrogen) and strongly with high atomicnumber elements (e.g. metals). Consequently, their ability to provideinformation about low-density materials, in particular when in thepresence of higher density materials, is very poor. Neutrons do notsuffer from this limitation. They are able to pass easily through highdensity metals and provide detailed information about internal, lowdensity materials. This property is extremely important for a number ofcomponents that require nondestructive evaluation including engineturbine blades, munitions, spacecraft components, and compositematerials such as wind turbine blades. For all of these applications,neutron radiography provides definitive information that X-rays cannot.Neutron radiography is a complementary nondestructive evaluationtechnique that is able to provide the missing information.

Phoenix Nuclear Labs (PNL) has designed and built high yield neutrongenerators that drive a subcritical assembly, developed by SHINE MedicalTechnologies, to produce the medical radioisotope molybdenum-99 (“moly”for short). In some embodiments, such systems are adapted and modifiedfor neutron radiography indications. In some embodiments, the systemcomprises one or more the features described in sections I through Vabove to provide efficient, cost-effective, robust, safe, anduser-friendly neutron generation. In some embodiments, the system isfurther modified as described below.

The neutron generator used in this example was originally designed forthe production of medical isotope and as such, requires a relativelyhigh neutron yield. The amount of neutron radiation generated is aboveallowable levels for nearby personnel and thus the radiation generatingportion of the device should be placed underground. Because part of thedevice is then underground, there is very limited space with which toconfigure the radiography system.

While the neutron yield of the PNL generator is very high for its sizeand cost, it is several orders of magnitude lower than for a typicalneutron radiography facility, e.g. a nuclear reactor. Therefore, theneutron-detecting medium should be in close proximity to the neutronsource. Conversely, at a nuclear reactor, it is typical that thedetection medium can be several meters away from the neutron source,allowing for space in which to place filters to mitigate undesirabletypes of radiation, mainly stray gamma rays, which will partially blurthe image during acquisition.

For the PNL system, the close proximity of the neutron detector resultsin a large flux of gamma radiation, since it decreases roughly with theinverse square of the distance from the source, while precluding the useof enough gamma-filtering materials such as lead or bismuth, which isexacerbated by the limited space available underground in the PNLsystem.

The PNL system uses deuterium-deuterium fusion to generate neutrons anddoes not produce gamma rays in the initial reactions. It is thesubsequent reactions between the neutrons and surrounding materials thatare of interest. The radiography setup has a neutron guide (e.g.,collimator), layered on the inside with cadmium sheeting, which is ahighly neutron-absorbing material. This ensures that neutrons not aimedstraight at the detector will essentially be excluded from the beam. Insome embodiments, where two gold foils are employed, one is covered withcadmium to simulate a standard neutron activation analysis technique todetermine the composition of thermal and fast neutrons in the beam.However, the cadmium releases a 550 keV gamma ray following the neutronabsorption process. This gamma ray can strike the detector and causesome fogging of the image. This is an unavoidable process and should bedecreased as much as possible.

On the outside of the neutron guide (e.g., collimator), there is a verylarge neutron population comprised of a spectrum of energies between 0and 2.45 MeV. It is generally the lower energy neutrons that are used inthe imaging process and so it is desirable to decrease the energy of theneutrons as much as possible. However, these lower energy neutrons aremore likely to produce subsequent gamma rays when absorbed bysurrounding materials, as in the case of the cadmium. Low-energyneutrons cause these gamma production events whether they are inside oroutside of the neutron guide r. Since it is only the neutrons inside theguide that are useful for the image acquisition, the neutrons outsidethe guide should be absorbed as well. This is accomplished herein by alayer of borated polyethylene (BPE), which absorbs the neutrons beforethey can cause gamma producing events in the cadmium. The boron, though,emits a 478 keV gamma ray, which can be absorbed easily by a layer oflead between the BPE and the neutron guide walls. In some embodiments,the borated polyethylene (BPE) on the collimator is conical in shape,extends the length of the collimator (e.g., approximately 40 inches),and is 1 inch thick. The BPE on the imaging box where the images arecollected is rectangular in shape, surrounding the box on all sidesexcept for the opening where the collimator end is, and is also 1 inchthick.

Some neutrons can traverse the borated polyethylene to still producegamma events in the cadmium. These are known as epithermal neutrons andalso should be mitigated. In order to slow these neutrons down toenergies that allow for absorption, a 6-inch layer of high densitypolyethylene (HDPE) has been added, surrounding the layer of BPE. Insome embodiments, the HDPE layer is from 4 to 8 inches thick. The HDPElayer aids in moderation of the epithermal neutrons to thermal energiesso that they are absorbed by the boron in the BPE without ever reachingthe cadmium layer. Further, a diffusion region comprised of air has beenintroduced that allows for relatively the same optical path length forthermal neutrons to enter the aperture of the collimator, whileincreasing the distance that fast neutrons must traverse beforeentering. In some embodiments, the air diffusion region is 6 cm long and2.5 cm in diameter. This longer path length for fast neutrons allowsthem more opportunities to scatter in the moderating medium and thus beslowed to more thermal energies. Alternative materials such as water andgraphite may be used in place of the HDPE, although HDPE provides a morecost-effective material that can be readily machined.

Finally, the collimator has been offset so as not to “look” directly atthe fast neutron source. This ensures that what the collimator “sees”will be more of the thermal neutron population, reducing the fastneutron content through the aperture. In some embodiments, thecollimator is offset both radially and tangentially from the neutronsource in order to not have direct line of sight to the neutron sourceand to also place moderating material between the collimator apertureand the neutron source. In some embodiments, it is offset by 17 cmradially and 14 cm tangentially. The position is found by observingwhere the highest population of thermal neutrons exists and then placingthe collimator aperture into that region. The placement of thecollimator then disrupts the population. Further shifting is performedto find the location that produces the highest thermal neutronpopulation at the opposite end of the collimator.

The MCNP (Monte Carlo N-Particle) transport code has been used tosimulate the neutron transport and gamma ray generation from neutroncapture in the various materials. The simulation utilizes libraries ofnuclear data from calculated and empirical data for scattered andabsorbed radiation. The simulation suite has been available for decadesand is continually being updated and enhanced.

Various moderation materials have been tested, including light water,heavy water and graphite, in attempts to increase the available thermalneutron flux on the gold foils, reduce the fast and epithermal flux onthe foils and reduce the gamma rays at the end of the collimator. Foilmeasurements have been attempted to verify that the model itself isconverging on accurate predictions.

Optimization of the MCNP models has been carried out to determineoptimum thicknesses of HDPE, BPE, lead, moderator material and geometry,and the diffusion region. This optimization has revealed practicalgeometries in terms of sizes and weight. One great difficulty with sucha heavily shielded geometry is that neutron transport through thecollimator aperture is very low, approximately 7 orders of magnitudelower than the neutron source production. In order to obtain high enoughcounting statistics for precise predictions, very long simulations mustbe run or very clever particle weighting must be performed.

The first tests were performed only with blocks of graphite asmoderating material with no BPE or HDPE on the outside layers of thecollimator. It was found then that many fast neutrons could streamthrough the interstitial spacing between the blocks of graphite,increasing the fast neutron population at the image plane. It was alsorealized that the thermal neutrons outside the collimator were creatinga massive population of gamma rays from the inner layer of cadmium dueto a lack of shielding on the outside of the collimator.

Water was then added to the system to fill in all the cracks in thegraphite and provide a 100% full moderator. The water, however, is arelatively highly absorbing material of thermal neutrons and so whilethe fast neutron flux went down, so did the thermal neutron population.A partially heavy water moderator was built into the graphite stack.Heavy water is both highly scattering and lightly absorbing of neutrons,making for an outstanding moderating material. The thermal neutronpopulation was found to increase, while the fast neutron populationstayed relatively constant. However, heavy water is very expensive andan ideal configuration of this material for a moderator was impractical,especially not submerged in light water.

As stated previously, the fast and thermal neutron population is veryhigh and especially so in the very close proximity that must be workedwith in the underground chamber. Due to this limitation, very carefullychosen shielding must be used to block both thermal neutrons andthermalize the fast neutron population. The embodiments described hereinachieve this result.

An exemplary configuration is shown in FIG. 24 that provides anexcellent solution for a high thermal/low fast neutron flux, whilereducing the gamma population at the image plane. Optimization of allgeometries should be performed to achieve the optimum thickness of HDPE,BPE, lead, moderator material and geometry, and diffusion region. Forone designed system, it has been determined that a large heavy watervessel should be used, surrounded by HDPE and BPE to optimize themoderator and shield the environment from unwanted radiation. This isconfigured as an above-ground system, but the image plane is still inthe near vicinity of the neutron source. Because of this configuration,the careful design described herein is needed to enhance the desiredradiation features while suppressing the unwanted radiation such asgamma rays and fast neutrons.

B. Semiconductor Fabrication

The systems and methods described herein (e.g., using a hydrogen ionparticle accelerator) find use in semiconductor fabrication. Suchsystems find use, for example, in the formation of thin films ofmaterial from a bulk substrate. The thin film of material is separatedfrom the bulk substrate by generating a cleave region formed byparticles implanted from a hydrogen ion particle beam and then cleavingat the cleave region. In some embodiments, the thin films are wafer usedin the production of solar panels (e.g., solar grade photovoltaic (PV)wafers) or light emitting diodes (LEDs). The wafers may be of anydesired shape (e.g., circular, square, or rectangular). The wafers maybe of a thickness of less than 100 micrometers. In some embodiments, thewafers have a thickness of 2-70 microns. In some embodiments, the wafershave a thickness of 4-20 microns.

Silicon wafers have conventionally been produced by first creating asingle crystalline cylindrical ingot of silicon (see e.g., U.S. Pat. No.9,499,921, herein incorporated by reference in its entirety). In oneexample, circular wafers are sliced off the end of the cylindrical ingotby a diamond coated wire. The diamond coated wire is typically about 20micrometers in diameter. This method of producing wafers by slicing thewafer off of the end of the cylindrical ingot creates a waste of thethickness of the diamond coated wire, or about 20 micrometers, byshaving that amount of the thickness into dust. In other examples, thecrystalline cylindrical ingot is trimmed to a square or rectangularshape by squaring the ingot into an elongated rectangular box shapeabout 1.5 meters long. In the process of squaring the ingot, valuablematerial is removed as waste material. Because the costs of materialscan dramatically influence adaptation of certain products andtechnologies, such waste and inefficiency can have significantimplications.

The systems provided herein, because of their cost effectiveness,efficiency, robustness, safety, and other desired parameters permit thegeneration of desired semiconductor materials at previously unattainablescales and efficiencies, reducing overall manufacturing costs andfacilitating expanded markets for such materials. The high-energy ionbeam systems described herein may be integrated as the source ofhydrogen ions into existing fabrication systems and processes. Forexample, existing systems that employ a high-energy ion beam generatorintegrated with a wafer manufacturing component can substitute their ionbeam generators for those described herein. Examples of such systemsinclude, but not limited to, those of U.S. Pat. App. Nos. 2015/0340279,2015/0044447, and 2016/0319462, U.S. Pat. Nos. 7,939,812, 7,982,197,7,989,784, 8,044,374, 8,058,626, 8,101,488, 8,242,468, 8,247,260,8,257,995, 8,268,645, 8,324,592, 8,324,599, 8,338,209, 9,404,198, and9,499,921, and in the SIGEN POLYMAX systems (see, e.g., Kerf-less waferproduction, Sigen, Photon's 4th PV Production Equipment Conference, Mar.4, 2009), SOITEC SMART CUT systems (see, e.g.,www.soitec.com/en/products/smart-cut), and AXCELIS high energy implantsystems in the PURION, OPTIMA, and PARADIGM SERIES systems (see, e.g.,www.axcelis.com/products/high-energy, and Felch et al., Ion implantationfor semiconductor devices: The largest use of industrial accelerators,Proceedings of PAC2013, Pasadena, Calif. USA), the disclosures of whichare herein incorporated by reference in their entireties.

All publications and patents provided herein incorporated by referencein their entireties. Various modifications and variations of thedescribed compositions and methods of the invention will be apparent tothose skilled in the art without departing from the scope and spirit ofthe invention. Although the invention has been described in connectionwith specific preferred embodiments, it should be understood that theinvention as claimed should not be unduly limited to such specificembodiments. Indeed, various modifications of the described modes forcarrying out the invention that are obvious to those skilled in therelevant fields are intended to be within the scope of the presentinvention.

1. A neutron generator system comprising: a) an accelerator thatproduces an ion beam; b) a gas target positioned to be contacted by theion beam; c) a target aperture separating said accelerator and said gastarget; and d) a reverse gas jet, at said target aperture, thatincreases pressure differential across said aperture.
 2. The system ofclaim 1, wherein said reverse gas jet comprises a nozzle that divergesafter it converges.
 3. The system of claim 1, wherein said reverse gasjet comprises a nozzle aperture of approximately ⅜ inch.
 4. The systemof claim 3, wherein said reverse gas jet comprises a throat gap of lessthan 0.01 inch.
 5. The system of claim 4, wherein said reverse gas jetcomprises a nozzle angle of 12.5 degrees.
 6. A method of increasing apressure differential across a target aperture of a neutron generatorcomprising employing a reverse gas jet at said target aperture, whereinsaid neutron generator comprises: i) an accelerator that produces an ionbeam, ii) a gas target to be contacted by the ion beam, and said targetaperture, and wherein said target aperture separates said acceleratorand said gas target.
 7. The method of claim 6, wherein said reverse gasjet comprises a nozzle that diverges after it converges.
 8. The methodof claim 6, wherein said reverse gas jet comprises a nozzle aperture ofapproximately ⅜ inch.
 9. The method of claim 8, wherein said reverse gasjet comprises a throat gap of less than 0.01 inch.
 10. The method ofclaim 9, wherein said reverse gas jet comprises a nozzle angle of 12.5degrees.